ENGINEERING OF POWER PLANTS 



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ENGINEERING 



OF 



POWER PLANTS 



/^ BY 
ROBERT H. FERNALD, M. E., A. M., Ph. D. 

WHITNEY PBOFE8SOR OP DYNAMICAL ENQlNEBBINa, TTNIVERSITY OF PENNSYLVANIA. 

AND 

GEORGE A. ORROK, M. E. 

CONSULTING ENGINEER, NEW YORK 
FORMERLY MECHANICAL ENGINEER THE NEW YORK EDISON COMPANY 



Second Edition 



MgGRAW-HILL book COMPANY, Inc. 

NEW YORK: 370 SEVENTH AVENUE 

LONDON: 6 & 8 BOUVERIE ST., E. C. 4 

1921 









Copyright, 1916, 1921, by the 
McGraw-Hill Book Company, Inc. 



^f-(?%^ ^^ 



§)CI.A611757 

Tax: MAPiiH psEss X o » h: pa 

APR 21 1921 



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PREFACE TO SECOND EDITION 

In preparing the second edition of Engineering of Power Plants 
onh^ corrections, slight modifications and reasonable additions have 
been made. 

Owing to unstable commercial conditions no attempt has been 
made to bring prices down to date. The prices given are, therefore, 
pre-war figures, except when expressly stated to the contrary. If used 
for other than illustrative instructional purposes they should be modi- 
fied to meet the conditions prevailing at the time. 

R. H. F. 
G. A. 0. 

December, 1920. 



vu 



PREFACE TO FIRST EDITION 

This work is not a treatise on power plants. 

It is simply an epitome of the subject arranged by the authors for 
convenient classroom use. 

Originally compiled by one of the authors in 1908 for use at the Case 
School of Applied Science, these notes have been used for eight years at 
that institution and for four years at the University of Pennsylvania as 
the fundamental course in power plants for all senior engineering students, 
including mechanical, electrical, chemical, civil and mining engineers. 

Besides offering much general material relating to the Engineering of 
Power Plants, the two underlying thoughts in the preparation of this 
text for classroom use have been — 

(a) To bring to the student a realization of the fact that engineering, 
although based on the exact sciences, is not itself an exact science but 
requires, on the part of the successful engineer, a natural fund of " common 
sense" and the application of engineering judgment — a realization of the 
fact that accuracy may mean within twenty per cent, and not the seventh 
place to the right of the decimal point; and 

(6) To give the student some idea of the commercial side of engineer- 
ing — a field too seldom touched upon in many engineering courses. 

The cost figures presented must be used with caution as market 
variations are such and local conditions so different that such data can 
be at best only approximate. 

Although the authors have endeavored to give credit for data copied 
from various sources, much of the material has been so subdivided 
and used by so many different writers that it has not been feasible to 
trace it to its original source. 

The authors desire to acknowledge their appreciation of the excellent 
service rendered by Paul J. Kiefer in checking the material presented in 
these notes. R. H. F. 

G. A. 0. 



CONTENTS 

Page 

Preface vii 

Chapter 

I. Sources of Energy 1 

II. The Steam Engine .........'. 18 

III. Efficiency and Cost of Electric Generators and Motors 77 

IV. Foundations 83 

V. Condensers 87 

VI. The Steam Boiler 121 

VII. Chimneys and Mechanical Draft 166 

VIII. Smoke and Smoke Prevention 190 

IX. Boiler Auxiliaries 1966 

X. Piping 215 

XI. Coal and Ash Handling . . 232 

XIL The Steam Power Plant ' . . . 239 

XIII. Variable Load Economy 269 

XIV. Cost of Power 285 

XV. Hints on Steam Plant Operation 316 

XVI. Power Transmission 320 

XVII. District Heating 334 

XVIII. The Power Plant of the Tall Office Building 347 

XIX. The Power Plant of the Steam Locomotive 355 

XX. Fuels 366 

XXI. Internal-combustion Engines 402 

XXII. Producer Gas and Gas Producers 439 

XXIII. Comparative Efficiencies and Operating Costs for Different Types of 

Installations 496 

XXIV. Compressed Air 519 

XXy. Refrigerating Machinery . 533 

XXVI. Hydraulic Power 538 

Index 579 



IX 



ENGINEERING OF POWER 
PLANTS 

CHAPTER I 
SOURCES OF ENERGY 

For industrial purposes energy is derived from : 

(a) Vital forces; muscular power of men and animals. 
(6) Gravity; energy of the wind and flowing water. 

(c) Chemical forces; energy of fuel. 

In considering the various types of power, it is convenient to further 
subdivide item (c) into: 

(d) Steam. 

(e) Gas. 

(/) Compressed air. 

(g) Hydraulic power; with application to pumps, elevators, cranes, etc. 

(h) Electric. 

Unit of Power. — The unit^ of power is the horsepower (hp.). One 
horsepower = 33,000 ft.-lb. per minute or 550 ft.-lb. per second in 
American and Enghsh practice. The metric horsepower used in Europe 
= 542.47 ft.-lb. per second or 0.9863 English horsepower. The metric 
horsepower is known as the pferde starke (P.S.) in German and cheval 
de vapeur in French. The unit used in electrical measurements of 
power is international and is called the watt, of which 746 correspond 
to the mechanical energy in 1 hp. The metric horsepower = 736 watts. 

Efficiency of a Machine. — Kent states that the efficiency of a machine 
is a fraction expressing the ratio of the useful work to the whole work 
performed, which is equal to the energy expended. The limit to the 
efficiency of a machine is unity, denoting the efficiency of a perfect 
machine in which no work is lost. The difference between the energy 
expended and the useful work done, or the loss, is usually expended 
either in overcoming friction or in doing work on bodies surrounding 
the machine from which no useful work is received. Thus in an engine 
propelling a vessel part of the energy exerted in the cylinder does the 
useful work of giving motion to the vessel, and the remainder is spent in 
overcoming the friction of the machinery and in making currents and 
eddies in the surrounding water. 

^ In 1913, Mr. H. C. Stott suggested a double unit called the Myriawatt as a 
standard for steam-electric power. This standard has not yet been adopted. For 
discussion, see Journal A. S. M. E., February, 1913. 

1 



2 ENGINEERING OF POWER PLANTS 

A common and useful definition of efficiency is ''output divided by 
input." 

Muscular Power of Men and Animals. — In dealing with living motors, 
it must be borne in mind that the motors are seldom alike, that the same 
motor varies at different times and that such motors can be used only 
intermittently as rest is absolutely essential. 

The various treatises on the subject point out that such motors will 
differ with: 

(a) The health of the specimen, his muscular development, his nervous tempera- 
ment, his disposition, his degree of stimulus of interest and will. 
(6) The species of animal, the race of man. 
(c) The amount of practice, the degree of training. 
{d) The abundance of food and air; the climate. 

These items are all important but it is hardly possible, to determine 
their exact effect upon the motor. 

The more tangible elements that effect the work accomplished are: 

(c) The relation of the working hours to those of rest in the 24 hr. of the day. 
(/) The relation between the maximum exertion possible and the force actually- 
exerted. 

(g) The speed in feet per second. 

(h) The nature of the machine receiving the effort of the motor force. 

The effort of the application of energy should be to secure the greatest 
foot-pounds in a continuous day's work. 

Labor of Men. — Man's labor is usually in lifting, pushing or pulling, 
or in transporting weights. Experimental data are as follows: 



Work of Men against Known Resistances (Rankine) 



Kind of exertion 



Resist- 
ance, lb. 



Velocity, 
ft. per 



Hours 
per 
day 



Ft,-lb. 
per sec. 



Ft.-lb. 
per day 
(8 hr.) 



1. Raising his own weight up stair or ladder 

2. Hauling up weights with rope and lowering the 
rope unloaded 

3. Lifting weights by hand 

4. Carrying weights upstairs and returning un- 
loaded. 

5. Shoveling up earth to a height of 5 ft. 3 in 

6. Wheeling earth in barrow up slope of 1 in 12}-^, 
horiz. veloc. 0.9 ft. per sec, and returning un- 
loaded 

7. Pushing or pulling horizontally (capstan or oar) 



8. Turning a crank or winch. 



9. Working pump. 
10. Hammering. . . . 



143.0 



40.0 
44.0 



143.0 
6.0 



132.0 
26.5 
12.5 
18.0 
20.0 
13.2 
15.0 



0.5 



0.75 
0.55 



0.13 
1.3 



0.075 
2.0 
5.0 
2.5 
14.4 
2.5 
? 



10 



10 



8 

2 min, 

10 

8? 



71.5 



30.0 
24.2 



18.5 

7.8 



53.0 
62.5 
45.0 
288.0 
33.0 



2,059,200 



648,000 
522,720 



399,600 
280,800 



356,400 
1,526,400 

1,296,000 

1,188,000 
480,000 



Note. — See Taylor's study on "Handling Pig at Bethlehem," "Principles of 
Scientific Management," Harpers, 1911, p. 25. 



SOURCES OF ENERGY 3 

Records show that men have pulled once 182, 208, 227 and 267 lb. 
Ordinarily, at a crank a man will exert from 15 to 18 lb. continuously 
and from 25 to 30 or even 40 if applied intermittently. Such a crank 
will turn from 26 to 30 revolutions per minute. 

At 18 lb., the foot-pounds per day are 1,296,000, while for an engine 
horsepower they are 15,840,000, or the man has one-twelfth or one- 
thirteenth the power of an engine horsepower. 

Clark says that the average net daily work of an ordinary laborer 
at a pump, a winch, or a crane may be taken at 3300 ft.-lb. per minute, 
or J^o hp., for 8 hr. a day; but for shorter periods from four to five times 
this rate may be exerted. 

Rowing in races is calculated to exact 4,000 lb. raised 1 ft. high per 
minute, or nearly J^ hp. 

The action of the heart limits the stress which can be put on the 
human organism. For a short time like 23^ min., records of 11,550 
ft.-lb. per minute have been recorded, but usually 3,000 ft.-lb. per 
minute is too high for acceptable service. 



Performance of Men in Transporting Loads Horizontally 
(Rankine) 



Kind of exertion 



Load, 
lb. 



Velocity, 
ft.-sec. 



Hours 
per 
day 



Lb. con- 
veyed. 
1 ft. per 
sec. 



Lb. con- 
veyed, 1 ft. 
per day 



11. Walking, unloaded, transporting his own weight. 

12. Wheeling load L in 2-whld. barrow, return un- 
loaded 

13. Wheeling load L in 1-wh. barrow, return un- 
loaded 

14. Traveling with burden 

15. Carrying burden, returning unloaded 

16. Carrying burden, for 30 sec. only < 



140 

224 

132 
90 
140 
252 
126 




5.0 

m 
m 

0.0 
11.7 
23.1 



700.0 

373.0 

220.0 
225.0 
233.0 

0.0 
1,474.2 

0.0 



25,200,000 

13,428,000 

7,920,000 
5,670,000 
5,032,800 



Coignet's apparatus was a hoist, in which dirt on one platform was 
lifted 'out of an excavation by the descent of laborers on a similar plat- 
form attached to rope passing over a pulley at the top. The laborers 
lifted their weight out of the excavation by climbing up ladders, and 
their descending weight over-balanced the material to be lifted. Brakes 
controlled the speed. 

Where weights are lifted by men hauling over pulleys, about 40 lb. 
is an average pull. 

Emerson states that to spade up a section of land would take an 
active man's energy for 500 years. With oil power tractors and gang 
plows three men can turn over 640 acres of land in 36 hr. It is good 
hard work to make a broad jump of 20 ft. at a speed of 10 miles an hour, 



4 ENGINEERING OF POWER PLANTS 

rising 4 ft., from the ground, but aeroplanes at the international contest 
this year (1912) will fly 80 miles at a speed which may reach 110 miles' 
an hour, and fly as easily at an altitude of 5,000 ft. as at 50. Formerly 
a man could carry a maximum load of 100 lb.; today his trains drag 
6,000 tons and his ships carry 30,000 tons. 
As pointed out by Greenfield^ 

*'One of the serious objections to the use of man-energy for motive purposes 
lies in the impracticability of securing large amounts of power from even large 
groups of men. A little calculation will make this point clear: The power plant 
of a modern "department store" may contain, let us say, eight steam boilers with 
an aggregate capacity of some 4,800 hp. To produce 5,000 hp. by the use of men 
it would be necessary to employ 5,000 X 10 = 50,000 men, who are supposed to 
drive the electric generators, tread wheel fashion. Assigning a floor space of 2 
ft. by 4 ft. to each man, these workers would require a total floor space of 50,000 
X 8 = 400,000 sq. ft., which is about one-fifth of the total floor space in the 
Philadelphia store of John Wanamaker." 

This point will be more fully emphasized by the following illustration. 

The total indicated horsepower of the turbine steamer Mauretania is 70,000. 
If the average demand is 60 per cent, of her rated horsepower, how many men would 
be required for a trans- Atlantic trip -if man-power were substituted for the turbines 
on this steamer? 

The most efficient way to use a man's effort is to have him lift his 
own weight, either by treadmill, tread-power or by using his weight as 
a counterpoise for the dead weight to be lifted. Here he does 4,000 
ft.-lb. per minute as a counterweight or in treadmills, 3,000 ft.4b. 2,600 
to 2,750 ft.-lb. is a figure for use with a crank. 

A heavy flywheel (200^00 lb.) is very useful in machines for human 
motors to equalize the unequal effort in parts of the revolution where 
the man can exert but little power. 

All things considered a man seems to be most efficient for continued 
service when he works one-third of his day of 24 hr. at a speed of one- 
third of his maximum and exerts one-third of his maximum force. 

Animal Motors. — 



Work of Horses against a 


Known Resistance (Rankine) 




Kind of exertion 


Resist- 
ance, lb. 


Velocity, 

ft. per 

sec. 


Hours 


Ft.-lb. 
per sec. 


Ft.-lb. 
per day 


1. Cantering and trotting, drawing a light rail- 
way carriage (thoroughbred) 

2. Horse drawing cart or boat, walking (draught- 
horse 


min. 221.^ 
mean 30}-^ 
max. 50 

120 

100 

66 


14% 

J 

3.6 
3.0 
6.5 


4 

8 
8 


44 7 H 

432 
300 
429 


6,444,000 

12,441,600 
8,640,000 




6,950,000 







1 Cassiers Magazine, 1911, "Human Energy as a Motive Power" by B. S. Green- 

FIE>LD. 



SOURCES OF ENERGY 



5 



Kent states that the average power of a draught-horse, as given 
in Hne 2 of the above table, being 432 ft.-lb. per second, is 432/550 = 
0.785 of the conventional value assigned by Watt to the ordinary unit of 
the rate of work of prime movers. It is the mean of several results of 
experiments, and may be considered the average of ordinary performance 
under favorable circumstances. 

Performance of Horses in Transporting Loads Horizontally (Rankine) 



Kind of exertion 



Load, 
lb. 



Velocity, 

ft. per 

sec. 



Hours 
per 
day- 



Trans- 
port 
per sec. 



Transport 
per day 



Walking with cart, always loaded 

Trotting with cart, always loaded 

Walking with cart, going loaded, returning 

empty; V, mean velocity 

Carrying burden, walking 

Carrying burden, trotting 



1,500 
750 

1,500 
270 
180 



3.6 

7.2 

2.0 
3.6 

7.2 



10 

10 
10 

7 



5,400 
5,400 

3,000 

972 

1,296 



194,400,000 
87,480.000 

108,000,000 
34,992,000 
32,659,200 



This table has reference to conveyance on common roads only, and 
those evidently in bad order as respects the resistance to traction upon 
them. 

A horse towing or drawing at a walk will average a pull of 120 lb. 
at 33^ ft. per second or 2.3 miles per hour. At a trot the pull will be 
but 66 lb. at 6J^ ft. per second. 

In a whin or gin at a brisk walk, or at 3 ft. per second, the pull will 
be about 100 lb. The curved track lowers the efficiency of the draft. 
Forty feet is the usual diameter of circle for large machines. In towing 
the average figures are: 



Miles per 
hour 


Hours per day 


Load in tons 


Miles per hour 


Hoiu-s per day 


Load in tons 


2.5 


11.5 


520.0 


6.0 


2.0 


30.0 


3.0 


8.0 


243.0 


7.0 


1.5 


19.0 


3.5 


5.9 


153.0 


8.0 


1.12 


13.0 


4.0 


4.5 


102.0 


9.0 


0.75 


9.0 


5.0 


2.9 


52.0 


10.0 


0.55 


6.3 



In horse power or horse gears the slow speed of the motor requires 
multiplying mechanism for high-speed machinery. The losses here Hmit 
the field for these motors. 

Although the engine horsepower is 33,000 ft.-lb. per minute, the 
living horse does not keep this rate up all day. In pumping with horses 
the records are : 

23,412 ft.-lb. per 8 hr. per day. 

24,360 ft.-lb. per 6 hr. per day. 

27,056 ft.-lb. per 4.5 hr. per day. 

32,943 ft.-lb. per 3 hr. per day. - 



6 ENGINEERING OF POWER PLANTS 

The average is from 21,000 to 25,000 ft.-lb. per minute. 

Other animals used for draught purposes are the ox, the mule, the 
ass, the elephant, the reindeer and the dog. The ox-power is about 
12,000 ft.-lb. per minute, the mule 10,000; the ass 3,500. Rankine 
favors two-thirds speed and same load for the ox as compared with the 
horse; for the mule one-half load and same velocity; for the ass one- 
quarter load and same velocity as for the horse. 

For transporting burdens the camel, the dromedary and the llama 
may be added to the list. 

The load of a freight camel is 550 lb. carried 30 miles per day for 4 
days; for dromedary the load is 770 lb.; the llama, 110 lb. 

Animal motors are used in frontier or colonial conditions for farming 
and forest service; for crushing and grinding sugar, for cotton work, for 
sawing, pumping, irrigation, etc.^ 

GRAVITY— ENERGY OF WIND AND WATER 

Windmills. 2 — Horizontal-shaft four-sailed windmills of the ''Dutch" 
type have been used for many years. A few vertical shaft wheels have 
also been used. These types, although efficient, were costly and hard 
to control and have been superseded by the ''American" type which has 
spread over the entire globe. 
If 

P = wind pressure in pounds per square foot, 
V — wind velocity, miles per hour, then from Stanton's ex- 
periments, 

P = 0.0036F2 

If D = diameter of wheel in feet, 

^r = work in foot-pounds per second, then for European mills of 

the Dutch type, 
W = OmilDW^ (Coulomb) 

This value of W is likely to be higher than shown by average 

practice. 

For mills of the American type 
W = 0.000451)273 (Wolff) 
W = 0.000502)273 (Griffiths) 

1 See A.S.M.E., vol. 14, p. 1014, paper by Thomas H. Brigqs, ''Haulage by 
Horses." 

2 Note. — Among early experimenters the work of Smeaton and Coulomb stands 
out conspicuously. Excellent theoretical treatments will be found in "Windmills" 
by A. R. Wolff and in the Encyclopedia Britannica, 11th edition by W. C. Unwin. 

See also "Modern Tests" in Water Supply Papers Nos. 1 and 8, U. S. Geological 
Survey. For wind-pressure formulas, see Stanton in Proceedings I.C.E., vol. 156 
and works of Eiffel and Hagen, 



If 

hp. 



then 



SOURCES OF ENERGY 



horsepower, 



hp. = 



853,000 




Fig. 1. 



The efficiency of modern wheels varies from 5 to SO per cent., 10 to 
18 per cent, representing standard practice. Much of the power is 
lost in the gearing. 

The best wind velocity is about 15 miles per hour, the useful range 
being from 10 to 20 miles. 

The best wheel diameter seems to be about 12 ft., although wheels 



8 



ENGINEERING OF POWER PLANTS 



from 8 to 16 ft. in diameter give excellent results; 80-ft. wheels have, 
however, been successfully used. 

A few wide blades are more efficient than many narrower ones. 
The vanes should not cover more than from 75 to 80 per cent, of the 
wheel area for best results and should never overlap. 

The governing of windmills is done almost entirely by putting the 
wheel into the plane of the wind. Certain foreign wheels govern by 
feathering the vanes and some American wheels by swinging sections of 
vanes into the plane of the wind. 

Windmills should be erected on towers or other elevated structures, 
but should not be set on hilltops or windy headlands. 

Reports of the U. S. Weather Bureau show that the useful hours 
(those with V between 10 and 20) are rarely over 3,000 per year in 
wooded locations, but in the Western plains and in certain favored 
localities in the East they may be much higher. 

Pumping is the best method of utilizing wind-power but many 
windmills are geared to run feed cutters and other agricultural machinery. 

Successful American manufacturers are reported by Wolff to be 
meeting the following guarantees. 

Capacity of Windmills.— 



Designa- 
tion of 


Vel. of 
wind, 

in miles 
per 
hour 


Revolu- 
tions 
of wheel 

per 
minute 


Gallons of water raised per minute 
to an elevation of 


Equiva- 
lent 
useful 
hp. de- 
veloped 


Average No. of 
hours per day 
during which 


mill 


25 

ft. 


50 

ft. 


75 
ft. 


100 

ft. 


150 

ft. 


200 

ft. 


these results will 
be obtained 


Wheel, ft. 


16 
16 
16 
16 
16 
16 
16 
16 


70 to 75 
60 to 65 
55 to 60 
50 to 55 
45 to 50 
40 to 45 
35 to 40 
30 to 35 


6.162 
19.179 
33.941 
45.139 
64 . 600 
97.682 
124.950 

212. asi 


3.016 
9.563 
17.952 
22.569 
31.654 
52.165 
63.750 
106.964 










0.04 
0.12 
0.21 
0.28 
0.41 
0.61 
0.78 
1.34 


8 


10 


6.638 
11.851 
15.304 
19.542 
32.513 
40.800 
71.604 


4.750 
8.485 
11.246 
16.150 
24.421 
31.248 
49.725 






8 


12 
14 
16 
18 
20 
25 


5.680 

7.807 

9.771 

17.485 

19.284 

37.349 


4.998 

8.075 

12.211 

15.938 

26.741 


8 
8 
8 
8 
8 
8 



In comparing Wolff's figures with those given by the formula it should 
be remembered that the values for horsepower as given in the table are 
overall horsepowers and include pump and pipe friction while the formula 
gives the horsepower available at the wheel shaft. 

For windmill economy, Wolff gives: 



SOURCES OF ENERGY 



Economy of Windmills.- 





Gal. of 
water 
raised 
25 ft. 
per hour 


Equiva- 
lent .ac- 
tual useful 

hp. 
developed 


Avg. No. of 

hours per 

day during 

which this 

quantity 

will be 

raised 


Expenses for 


actual useful power developed, 
in cents, per hour 




Desig- 
nation 
of mill 


For interest on 
1st cost (1st 
cost including 
cost of wind- 
mill, pump and 
tower 5 per 

cent, per 

annum) 


For repairs 
and deprecia- 
tion (5 per 
cent, of 1st 
cost per 
annum) 


For 
atten- 
dance 


For 
oil 


Total 


Expense 
per hp., 
in cents, 
per hour 


Wheel, ft. 




















8}i 


370 


0.04 


8 


0.25 


0.25 


0.06 


0.04 


0.60 


15.0 


10 


1,151 


0.12 


8 


0.30 


0.30 


0.06 


0.04 


0.70 


5.8 


12 


2,036 


0.21 


8 


0.36 


0.36 


0.06 


0.04 


0.82 


5.9 


14 


2,708 


0.28 


8 


0.75 


0.75 


0.06 


0.07 


1.63 


5.8 


16 


3,876 


0.41 


8 


1.15 


1.15 


0.06. 


0.07 


2.43 


5.9 


18 


5,861 


0.61 


8 


1.35 


1.35 


0.06 


0.07 


2.83 


4.6 


20 


7,497 


0.79 


8 


1.70 


1.70 


0.06 


0.10 


3.56 


4.5 


25 


12,743 


1.34 


8 


2.05 


2.05 


0.06 


0.10 


4.26 


3.2 



Based on the figures quoted by Wolff in the fifth column the cost of 
the installations including windmill, pump and tower is approximately. 



Wheel, 
ft. 



Cost, 

$ 



8.5 145 

10.0. 175 

12.0 210 

14.0 ....;.; 435 

16.0 670 

18.0 790 

20.0 1,000 

25.0 1,200 

American Windmill and Tower Prices 





Diam., 
ft. 


Mill alone 


Tower 




Rated 
hp. 


Rated 
r.p.m. 


Weight 

machinery, 

lb. 


Price 

f.o.b., 

Chicago 


Height, 

ft. 


Weight, 
lb. 


Price 

f.o.b., 

Chicago 


Wooden mill . . 


81/2 

10 
12 
14 
16 
18 
20 
25 


0.08 
0.12 
0.25 
0.40 
0.55 
0.75 
1.00 
1.25 


35 
35 
30 
28 
25 
22 
20 
16 


400 
500 
700 
1,010 
1,685 
1,880 
2,990 
4,300 


$28.50 

33.00 

42.00 

75.00 

114.00 

128.00 

194.00 

352.00 


20 
30 
40 
40 
40 
40 
40 
40 


203 
500 
950 
1.300 
1,450 
1,450 
2,935 
2,935 


$15.60 
30.00 
50.00 
82.50 
92.00 
92.00 
186.00 
186.00 


Steel mill 


8 
10 
12 


0.08 
0.12 
0.25 


30 
25 
20 


325 
500 
950 


22.50 
36.25 
66.00 


20 
30 
40 


203 
500 
950 


15.60 
30.00 
50.00 


Steel mill 


8 
10 
12 
14 
16 
20 


1.5-3 
2-4 
3-6 









30.00 

50.00 

70.00 

120.00 

175.00 

360.00 


25 
25 
25 
60 
60 
60 


435 

435 

585 

1,435 

2,550 

5,400 


26.50 
26.50 
38.50 
88.00 
160.00 
410.00 



10 



ENGINEERING OF POWER PLANTS 



Bulletin No. 105 of the North Dakota Agricultural Experiment Station 
contains a description of a 1.4-kw. electric light and power plant deriving 
its power from a 16-ft. aeromotor windmill on a 20-ft. wooden tower. 
In connection with the generator a 62-cell 40-amp.-hr., 110-volt Plants 
type storage battery 'is used. 

Cost of 16-ft. wheel, tower and governing pulley $200.00 

Cost of house 35 . 00 

Cost of dynamo 1.4 kw., 150 volts, 1,800 r.p.m 110 . 00 

Cost of battery 550 . 00 

Cost of switchboard 150 . 00 

$1,045.00 
Yearly charges: 

Interest, 6 per cent $62 . 70 

Dep. 10 per cent 104.50 

Attendance 12 . 80 

Oil 5.00 

Repairs 



$185.00 



Year 1912 — ^kilowatt-hours at switchboard per year 3,300. Cost per kilowatt-hour = 
5.6 cts. 

This wheel gave a maximum of 1,009 hp.-hr. in April and a minimum 
of 332 hp.-hr. in August. 

The two important factors in the success of this installation were the 
governor and an automatic regulator which cut the battery out and 
into the circuits as required. The attendance charged to the apparatus 
seems very small and the absence of repair charges is remarkable. 

Tide and Wave Motors. — Albert W. Stahl, U.S.N., finds^ the energy 
of ocean waves to be as follows: 



Total Enekgy op Deep-sea 


Waves 


IN Terms of Horsepower per Foot op 








Breadth 






Ratio of length 

of waves to 
height of waves 


Length of waves in feet 


25 


50 


75 


100 


150 


200 


300 


400 


50 


0.04 


0.23 


0.64 


1.31 


3.62 


7.43 


20.46 


42.01 


45 


0.05 


0.29 


0.79 


1.62 


4.47 


9.18 


25.30 


51.94 


40 


0.06 


0.36 


1.00 


2.05 


5.65 


11.59 


31.95 


65.58 


35 


0.08 


0.47 


1.30 


2.68 


7.37 


15.14 


41.72 


85.63 


30 


0.12 


0.64 


1.77 


3.64 


10.02 


20.57 


56.70 


116.38 


25 


0.16 


0.90 


2.49 


5.23 


14.40 


29.56 


80.85 


167.22 


20 


0.25 


1.44 


3.96 


8.13 


21.79 


45.98 


126.70 


260.08 


15 


0.42 


2.83 


6.97 


14.31 


39.43 


80.94 


223 . 06 


457.89 


10 


0.98 


5.53 


15.24 


31.29 


86.22 


177.00 


487 . 75 


1,001.25 


5 


3.30 


18.68 


51.48 


105.68 


291.20 


597.78 


1,647.31 


3,381.60 



^ See "The Utilization of the Power of Ocean Waves," Transactions A.S.M.E., 
vol. 13, p. 438. 



SOURCES OF ENERGY 11 

Commenting on the practical utilization of this form of energy he 
divides the subject into: 

1. The various motions of the water which may be utilized for power purposes. 

2. The wave-motor proper — that is, the portion of the apparatus in direct 
contact with the water, and receiving and transmitting the energy thereof; 
together with the mechanism for transmitting this energy to the pumping or 
other suitable machinery for utilizing the same. 

3. Regulating devices, for obtaining a uniform motion from the more or less 
irregular and variable action of the waves, as well as for adjusting the apparatus 
to the state of the tide and condition of the sea. 

4. Storage arrangements for ensuring a continuous and uniform output of 
power during a calm or when the waves are comparatively small. 

Taking up first the consideration of the motions that may be utilized 
for power purposes, we find the following: 

1. Vertical rise and fall of particles at and near the surface. 

2. Horizontal to-and-fro motion of particles at and near the surface. 

3. Varying slope of surface of wave. 

4. Impetus of waves rolling up the beach in the form of breakers. 

5. Motion of distorted verticals. 

Mr. Stahl further states : 

** Possibly none of the methods described in this paper may ever prove com- 
mercially successful; indeed the problem may not be susceptible of a financially 
successful solution. My own investigations, however, so far as I have yet been 
able to carry them, incline me to the belief that wave-power can and will be 
utilized on a paying basis." 

Wave motors are of two forms, the paddle type and the float type. 
In the former the paddle swings backward and forward with the wave 
motion, moving a shaft or pair of shafts by rachets. In the latter a 
heavy float is lifted by the waves and in falling drives a shaft by means 
of rachets. 

Many attempts in this direction have been made but no successful 
machine has been developed that can withstand the tremendous power 
of severe storms. 

A float-type motor erected near Los Angeles, Cal., developing suffi- 
cient power for about 30 incandescent electric lights, withstood the 
storms for one year. In this locality the waves, though high are 
regular. A storage battery was used for storing the energy developed 
during the day. 

There are several tide mill ponds along the Connecticut and New 
York shores. One such pond at Stamford is reported to have an area 
of some 10,000,000 sq. ft. One writer on the subject estimates that 
about 50 hp.-hr. can be realized per million square feet of pond area. 



12 ENGINEERING OF POWER PLANTS 

A plant that attracted much attention at the time of its construction 
is the hydrauHc air compressor of the Rockland Power Co., Rockland, 
Maine. The plant is described as follows : 

''The plant consists of two basins, a high- and a low-water one, as in the 
Decoeur system. Each basin has an area of 1 sq. mile and there is a tide of 10 ft. 
From the high-water basin a 15-ft. shaft extends vertically downward for 203 ft., 
and then is connected by a horizontal tunnel to a 35-ft. shaft extending upward to 
the low-water tank. At the top of the down-flow shaft there are 1 ,500 half -inch air 
inlet tubes, through which air is drawn into the water and carried to the bottom 
of the shaft. The air separates at the bottom and accumulates in an air chamber 
while the water flows up the larger shaft to the low-water tank. The air is under 
a head of water of 195 ft. and is piped to the surface through a 14-in. pipe which 
joins a 30-in. main. This apparatus develops 5,000 hp. and has an efficiency of 
75 per cent. It has no moving parts to break or get out of order. Air compressed 
by this method is very dry, -being about three times as dry as the atmosphere 
and this is a decided advantage as the pipe resistance of dry air is very low and 
velocities as high as 70 ft. per second may be used. Dry air also can be used cold 
for expansion purposes and will not freeze. As an actual test an 80-hp. Corliss 
engine was run for 10 hr. on this air, the admission temperature being 5.3°F. and 
the exhaust — 40°F. After the run there was no trace of frost in the exhaust port 
or passage. The only cost in connection with the operation of this compressor is 
the salary of a watchman to keep ice, timber, etc., from entering the inlet shaft. 
The construction cost of this particular plant amounted to about $100 per 
horsepower. Each basin of 1 acre, area and with a tide of 9 ft. can produce 
about 5 hp. A basin with an area of 200 acres and so located that it would not 
require more than 3 ft. of dam per acre would be a commercial success if de- 
veloped into an air-compressing plant." 

Apparently the most successful tide machines have taken advantage 
of the rising tide for storing water in tanks or basins from which it is 
passed through waterwheels or turbines. 

Solar Engines. 1— Using Herschell's data, Ericsson about 1870 esti- 
mated the direct heat energy of the sun in 45° latitude to be equivalent 
to 13,000,000 hp. per square mile. Buchanan in Egypt in 1882 by means 
of better apparatus recorded the extremely high rate of 3,245 B.t.u. per 
square foot per minute, which is equivalent to 214,000,000 hp. per square 
mile. 

Solar engines are not direct in their action, but use steam as an 
intermediary. The main interest is, therefore, in the boiler. 

Monehart's apparatus, exhibited in Paris in 1878, consisted of a 
conical mirror 112 in. in diameter, which concentrated the sun's rays 
on a boiler containing about 44 lb. of water. With 45 sq. ft. of reflecting 
surface he succeeded in evaporating 11 lb. of water from a feed tem- 
perature of 68°F. into steam at 75 lb. pressure. 

1 See Engineering News, May 13, 1909 and Nov. 17, 1910. 



SOURCES OF ENERGY 13 

Ericsson's apparatus consisted of a parabolic mirror 11 by 16 ft. 
which concentrated the sun's rays on a boiler 63-^ in. in diameter and 11 
ft. long. This machine, erected in New York in 1883, developed about 
3.25 hp. in a 6-in. diameter by 8-in. stroke engine. 

The steam was evaporated at 20 lb. gage pressure. A good condenser 
was used with this plant. 

Many similar machines have been built with varying success. Most 
of these machines were mounted on equatorial mountings and were 
swung to meet the sun but fixed boilers or rather evaporators have been 
proposed. Shuman in 1907 built at Tacony, Pa., an experimental plant, 
each unit of which consisted of a sheet-iron boiler 3 ft. square with a 



j 


ly 






1 




S/'riHi 


j 


tmm 


'M 


WKKIIa 


*^:-''W;4^^^ 


9 


iali 
Mm 




^^■'^#^"'''' 


ft 


w 


^p— 






•^ 


.||s.Jn^S 




" 


i 


m 


^ 



Fig. 2. — Original Shuman sun power plant, Aug., 1907, Tacony, Pa. 

water space J^ in. wide. This is placed on a table with a mirror on each 
side. The plant contained 26 banks of 22 units each, a total of 5,000 sq. 
ft. of boilers and 5,300 sq. ft. of mirrors, 10,300 sq. ft. in all. 4,800 lb. of 
water were evaporated in 8 hr. of sunshine at atmospheric pressure. A 
special engine was designed to work under this low range of pressures and 
from 20 to 32 hp. was developed. This plant was tested by Prof. R. C. 
Carpenter (see Engineer, London, July 5, 1912). 

Later Shuman in his plant at Meadi, Cairo, Egypt, went back to 
the moving parabolic mirrors with a 15-in. wide flat cast-iron boiler in 
the focus. This plant has five reflectors 204 ft. long, 133^ in. wide with 
a thermostat control to keep the axis in the sun's plane. The total re- 
flecting surface is 19,000 sq. ft. This plant averages 1,100 lb. of steam 
evaporated per hour for 10-hr. day. 

The engine at Tacony was a 24 by 24-in. special engine with extra 
large exhaust valves running 12-150 r.p.m. The Cairo engine was a 



14 ENGINEERING OF POWER PLANTS 

36 by 36-in. running at 110 r.p.m. The Cairo plant cost, exclusive of 
land, $7,600 or $140 per brake horsepower. 

Shuman figures that sun-power is economical in Egypt when coal 
costs more than $2.40 per ton. 

In the Shuman invention a tract of land is rolled level, forming a 
shallow trough. This is lined with asphaltum pitch and covered with 
about 3 in. of water. Over the water about }/q in. of paraffine is flowed, 
leaving between this and a glass cover about 6 in. of dead air space. It 
is estimated that a power plant of this type to cover a heat-absorption 
area of 160,000 sq. ft., or nearly 4 acres, would develop about 1,000 hp. 
Provision is made for storing hot water in excess of the requirements of 
a low-pressure turbine during the day, to be utilized for running the 
turbine during the period when there is no absorption of heat. The 
heated water is run from the heat absorber to the storage tank, thence to 
the turbine, through a condenser and back to the heat absorber. The 
water enters the thermally insulated storage tank, or the turbine, at 
about 202°F. With a vacuum of 28 in. in the condenser, the boiling 
point of the water is reduced to 102°, and as it enters the turbine nearly 
10 per cent, explodes into steam. Mr. Shuman estimates that a 1,000-hp. 
plant built upon his plan would cost about $40,000. 

Willsie's plant at the Needles, Cal., built in 1908-09, utilizes the sun's 
heat to vaporize sulphur dioxide through the medium of water heated in 
a pipe coil encased in glass. His apparatus developed 20 net hp. 

He figures his apparatus to cost as follows : 

400-hp. plant, per horsepower 

Solar heater $100 . 00 

Heat storage plant (100 hr.) 10 ! 00 

Engine and pumps 20 . 00 

SO2 vaporizers 15 . 00 

Condenser 15 . 00 

Emergency boiler 2 . 75 

SO2 1.25 

$164.00 
Operating cost per horsepower-hour 

Interest dep., etc 0.19 

Labor 0.27 

Supplies 0.15 

0.61 cts. 

Willsie compares the cost per horsepov/er-hour in a 400-hp., steam-electric 
and solar-electric power plant, and finds that the steam plant would 
have to obtain its coal for $0.66 a ton to compete with the sun-power 
plant in districts favorable to the latter. 



SOURCES OF ENERGY 



15 



The following table presents a brief summary of the development of 
the sun motor to date. 



Year 


Inventor 


Location 


Reflecting 
surface, 
sq. ft. 


Water 

evaporated 

per hour, lb. 


Square foot of reflect- 
ing surface per pound 
of evaporation 


1878 
1883 
1911? 
1913 


Mouchot 
Ericsson 
Shuman 
Shuman 


Paris 

New York 
Tacony 
Cairo 


45 

162 

10,300 

19,000 


11 

* 

600 
1,100 


4.09 

17.16 

17.28 



* 3.25 hp. developed in engine. 

The efficiency of the evaporative apparatus depends on the quality 
of the heat insulation. Ericsson's plant was much better in this regard 
than any of the others. Shuman's Tacony plant was nearly twice as 
good as the Cairo plant but was more costly. 

All modern plants use the steam at or near the atmospheric pressure 
and must have plenty of condensing water for the vacuum. It would 
appear that the turbine is the best form of apparatus to use steam 
between these limits. 

Prof. Fessenden's proposition (see British Association Adv. Science, 
1912) including windmills, turbines, a 1,000-ft. well, exhaust turbines 
and flat solar heaters, has not as yet been experimentally tried. 

Energy of Fuel. — In coal and other fuels an enormous capacity for 
doing work is stored in very compact bulk. It is liberated from the 
fuel gradually as required, and the limits of the available quantity 
have not yet been reached, although the time limit on anthracite coal 
and possibly other fuels appears to be close at hand. 

Such fuels are to be had in nearly all regions and where they are not 
native they are easily transported. If desired the energy resident in 
them can be transported in the form of gas to the place where it is to be 
used. 

It should not be forgotten that but a very small percentage of the heat 
energy in the fuel is actually converted into useful work at the machine. 
Roughly, if the fuel be used in a steam plant, 30 per cent, of the heat is 
lost by radiation and up the stack. Of the possible 70 per cent, that goes 
to the engine, nearly 90 per cent, is carried away by the condensing water 
or dissipated in the exhaust. Of the 10 per cent, or less converted into 
work a portion is used in overcoming friction, so that the useful work at 
the machine or busbars represents, in e^cient steam plants, between 
5 per cent, and 10 per cent, of the heat energy of the fuel thrown into 
the furnace under the boiler. 

In the latest large unit installations efficiencies of 17 and 18 per 
cent, have been reached^ but these are very exceptional. 



16 ENGINEERING OF POWER PLANTS 

Similar losses, although not necessarily of the same magnitude are 
evident in all present methods of power development from fuel. 

Analysis of Development in a Power Plant. — Hutton states that in 
the typical power plant there are five steps: 

1. Generation or liberation of the stored or accumulated energy. 

2. The storage or accumulation of the energy of heat thus liberated from the 
fuel in a suitable vessel or reservoir from which it can be drawn off as required. 
(In the steam plant this is the boiler.) 

3. The appliance whereby the energy stored in the boiler as potential energy 
is transformed into actual energy by being made to exert force through a pre- 
scribed path under the control of capable intelligence. (This is the engine.) 

4. The controlled force acting through the controlled space or path is to be 
transmitted from the engine or prime mover to the machine or apparatus which is 
to be driven. (This gives rise to mechanism and transmission machinery.) 

5. The industrial work of manufacturing, propelling or whatever may be the 
function of the generated power, is the last link in the chain. 

In water-power plants the liberation or storage of energy is done for 
the engineer before his work begins. This is also true of the windmill 
motor. In the gas, hot-air, or direct-combustion engine there is no 
storage step in the process, but the energy must be utilized as fast as it 
is released. On the other hand, for the gas-engine plant which produces 
its own gas there is a step of accumulation of energy which is lacking 
when solid fuel is burned directly under the boiler. 

D. B. Rushmore has estimated the amount of power used in the 
United States as follows: 

Horsepower 

Horses and mules 25,000,000 

Automobiles 25,000,000 

Steam and naval vessels 5,000,000 

Steam raUroads. 50,000,000 

Irrigation 500,000 

Mines and quarries 6,000,000 

Flour, grist and saw mills 1,250,000 

Manufactures 25,000,000 

Central stations 8,000,000 

Isolated plants , 4,250,000 

Electric railways 4,000,000 . 

Total 154,000,000 

Excluding the first four divisions, it is evident that about 49,000,000 
hp. are used in the ordinary manufacturing, heating, lighting and electric 
railway business. Of this power at least 25,000,000 hp. or over 50 per 
cent, is used in the form of electric energy. It is probable that nearly 



SOURCES OF ENERGY 17 

30,000,000 hp. are produced by steam; 12,000,000 hp. by water and 
about 7,000,000 hp. by gas or oil motors. 

The transmission of power in its various fields of electrical trans- 
mission, compressed air, high-pressure water, shafting, belting, gearing 
or linkage is an extensive subject in itself, but will be touched upon 
briefly later in these notes. 

Although the reciprocating steam engine may be regarded by many 
as obsolescent, it holds an important place in power production. Its 
mechanism and method of operation are better known by the average 
engineer than those of the more recent forms of prime movers. It is, 
therefore, used in these notes as a basis for the development of the 
essential principles of a power plant. 



CHAPTER II 



THE STEAM ENGINE 



Horsepower of a Cylinder. — 

Let P = pressure on piston in lb. per square inch. 
= mean effective pressure (m.e.p.). 
L — length of stroke in feet. 
A = area of piston in square inches. 
N = number times per minute that piston is acted upon by the 



then hp. = 



pressure. 
PLAN 
33,000 * 




Fig. 3. — Simple slide-valve engine, throttling governor. 

In an engine once constructed A and L are fixed or constant and 

the factor 33,000 is constant. If then K denotes the fraction ^r. r^r^ 

the hp. formula may be written hp. = PNK in which K is called the 
engine constant. 

It is not necessary that the piston travel back and forth in a straight 

18 



THE STEAM ENGINE 



19 



line, as in reciprocating engines, although this is the common type. 
When the piston or area receiving the steam pressure travels in a circular 
path continuously in the same direction the engine is called a rotary 
steam engine. 

The following handy rule is given for estimating the horsepower of a 
single-cylinder engine. 

Square the diameter and divide by 2. This is correct whenever 
the product of the mean effective pressure and the piston speed (in feet 
per minute) = 21,000. 



viz., when m.e.p. 
m.e.p. 
m.e.p. 
m.e.p. 



30 and S = 700. 
35 and S = 600. 
38 and S = 550. 
42 and S = 500. 




Fig. 4. — Simple steam engine. 



These conditions correspond to those of ordinary practice with both 
Corliss and shaft-governor high-speed engines. 

Length of Typical Reciprocating Engine. — Between head end and 
crankpin the length is made up of: 

(a) Cylinder = two cranks. 

(6) Piston rod = two cranks. 

(c) Connecting rod = six cranks (four to eight). 

(d) All allowances for stuffing-box, cylinder heads, metal in piston, 
crosshead, etc. 



20 



ENGINEERING OF POWER PLANTS 



Total = something over ten cranks. 

The oscillating engine, having no connecting rod, is only about four 
cranks long. 

The trunk engine, having no piston rod, is about five cranks long. 

Engines^ Classified by Position of Cylinder Axis. — (a) Horizontal; 
(6) Vertical; (c) Inclined. — Horizontal engines are most usual and cheap- 
est where room or floor space is not limited. 

Horizontal Engines.- — 

Advantages. — 

1. Cheapness. 

2. Convenience of access from ground level to all parts. 

3. Weight distributed over large area for support. 




Fig. 5. — Simple Corliss engine. 

Disadvantages . — 

1. Action of gravity adds to friction. Bad for stuffing-boxes. 
Piston springs often necessary. 

2. Tendency of cylinder to wear oval. 

Vertical Engines. — 

Advantages. — 

1. Diminished ground area. 

2. Avoidance of cyhnder friction and unequal wear. 

3. Require very little cylinder oil. 

The small ground-area requirement has made vertical engines prac- 

1 Much of the descriptive material relating to steam engines is from The 
Mechanical Engineering of Power Plants," by F. R. Hutton, John Wiley & Sons, 1908. 



THE STEAM ENGINE 



21 



tically universal for screw-propelled ships, which are deep-water vessels, 
and in crowded power plants in cities where ground is costly. 
Disadvantages. — 

1. Effort on crankpin is greater when weight of mechanism is 
acting downward with gravity. This must be counteracted 
to prevent unequal effort on crankpin and irregular speed. Three 
methods for accomplishing this are used: (a) counterweighting 
the crank on the side opposite the reciprocating parts; (6) steam 
cylinders so calculated as to balance; (c) by steam distribution 
to the two ends of the cylinder. 




Fig. 6. — Cross-compound vertical reversing engine. 



2. In large engines the different parts are on diiferent levels, 
or stories, increasing the number of men required to handle or 
superintend them. 

Beam Engines. — 

Advantages. — 

1. Steam cylinder can be vertical. 

2. Cylinder and its weight can be kept low down and shaft 
may also be directly attached to bedplate near the foundation. 

3. Long stroke for piston is possible and yet not too much 
space in ground plan consumed. Great advantage in side- 



22 



ENGINEERING OF POWER PLANTS 



wheel practice and pumping. R.p.m. may be kept low but 
piston speed high. 

4. Flexibility in alignment of cylinder a.xis in relation to shaft 
axis. 

5. Where there are several working cylinders, the beam makes 
easy means of operating them. Some cylinders vertical, others 
inclined, etc. 

Disadvantages. — 

1. Too many joints. 

2. Weight of beam so far above the center of gravity of the 
hull. 




Fig. 7. — Compound beam pumping engine. 

3. In warships, vulnerable part exposed. Destruction of this 
part fatal. This consideration resulted in the back-acting beam 
type. 

Classification of Engines by Their Use of Steam. — 

A. High-speed, low-speed, and moderate speed of rotation. 

B. Single- and double-acting. 

C. Expansive and non-expansive. 

D. Condensing and non-condensing. 

Ef Simple, compound or multiple expansion. 



THE STEAM ENGINE 23 

High-speed Engines. — Consequences of high rotative speed are: 

1. Small cylinder volume. 

2. Item 1 means engine light in weight. 

3. Short length of cylinder means a small crankarm, short 
connecting rod, and an engine short in length. 

4. Variations of either effort or resistance are more promptly 
met and less noticeable as compared with mean effort or resistance 
of any given minute. 

5. Regulating mechanism tends to equalize effort and re- 
sistance in less interval of time than with slower types. 

6. Decrease in economy with use, as valves cannot be kept tight. 

Low-speed Engines. — ^Limitations of speed are often imposed by 
the resistance to be overcome. This condition is met in pumping engines, 
blowing engines, paddle-wheel engine, marine engines, etc. It is possible 
to secure a large product of L X iV by making L large when N is small. 
Engines not making over 125 r.p.m. are classed as low-speed. 

Advantages of Low-speed are the Disadvantages of High. — 

1. Rapid alternating of admission and compression of steam 
through ports to cylinder of high-speed engine compel large port 
areas. 

2. Rapid motion of piston compels generous clearance allow- 
ance at each end between piston and cylinder heads. 

3. Wear per unit of surface greater in short stroke. 

4. Heating and abrasive wear goes on rapidly, resulting in 
possible increase in expense for maintenance and repairs in 
high-speed engines. 

5. Lubrication compelled to be generous to the point of waste- 
fulness in high-speed engines. 

6. The above five conditions compel a standard of workman- 
ship in fitting, alignment, provisions for wear, etc., which make 
high-speed engines costly to build and successful only when 
well made. 

Piston Speed as Distinguished from Rotative Speed.— 

Piston speed in feet per minute = L X N, 
Less than 500 ft. per minute = low speed. 
600 to 800 ft. per minute = moderate speed. 
Above 900 ft. per minute = high speed. 

As ma}^ readily be understood a low rotative speed engine does not 
necessarily have a low piston speed, as for example, an 18 by 48 Corliss 
engine making 85 r.p.m. Piston speeds as high as 1,400 ft. have been 
used. 



24 



ENGINEERING OF POWER PLANTS 



Single- and Double-acting Engine. — 

The single-acting engine takes steam on one side of the piston only. 
In the vertical engine of this type, the steam acts with gravity and in 
one direction only. 

This results in: 

(a) Silent running at high speeds. 

(6) Less danger of overheated bearings. 




Fig. 8. — Westinghouse single-acting engine. 



Single-acting vertical steam engines are usually made with twin 
cylinders. This construction gives a simple inexpensive engine. 

Although a few such types are still on the market, reduction of space 
occupied per horsepower of output and greater uniformity of turning 
moment on the crankpin have led to the general adoption of the double- 
acting principle. 

Expansive and Non-expansive Engines. — If steam is allowed to enter 
the cylinder at full boiler pressure during the entire stroke and is, at the 
end of the stroke, exhausted at this same pressure, the effort upon the 



THE STEAM ENGINE 



25 



piston has been constant and the steam has been used in the cylinder 
non-expansively. 

If, however, advantage is taken of the elastic quality of steam, it 
may be admitted to the cylinder at full boiler pressure for a portion of 
the stroke only and then allowed to expand during the remainder of 
the stroke. 

Under these conditions, the effort upon the piston decreases from the 
moment the steam supply to the cylinder is shut off until the end of the 
stroke. 

Single-cylinder direct-acting pumps and many elevator engines use 
steam non-expansively, but the majority of power-plant engines take 
advantage of the greater economy secured by operating expansively. 

Thermodynamic Efficiencies. — The increase in the thermodynamic 
efficiency by operating expansively and by condensing is readily seen by 
an examination of the following figures. 

If Ti = absolute temperature of steam entering the cylinder. 

T2 = absolute temperature of steam leaving the cylinder. 

Then 

Ti - T2 

efficiency = — ^ = efficiency of ''ideal" or Carnot cycle. 

i 1 





Steam-engine Efficiency 




Gage pressure, lb. 


Absolute pressure, lb. 


°F. = t 


°F. abs. = T 


-13 


2 


126 


586 


1 


16 


216 


676 


100 


115 


338 


798 


114 


129 


347 


807 


150 


165 


366 


826 


200 


215 


388 


848 



798 - 676 _ 122 

798 ~ 798 
807 - 676 _ 131 

807 ~ 807 
798 - 586 _ 212 

798 ~ 798 
826 - 676 _ 150 

826 ~ 826 
848 - 676 _ 172 

848 ~ 848 
826 - 586 _ 240 

826 ~ 826 



15.3 per cent, efficiency between 115 and 16 lb. abs. 
16.3 per cent, efficiency between 129 and 16 lb. abs. 
26.6 per cent, efficiency between 115 and 2 lb. abs. 

18.2 per cent, efficiency between 165 and 16 lb. abs. 

20.3 per cent, efficiency between 215 and 16 lb. abs. 
29.0 per cent, efficiency between 165 and 2 lb. abs. 



26 



ENGINEERING OF POWER PLANTS 



The steam engine cannot approach this ''ideal" or Carnot cycle. 
On this account it is customary to compare the thermal efficiency of 
the actual engine with a modified cycle known as the Rankine cycle with 
complete expansion. 

The outline of this comparison is as follows : 



Actual cycle = 
where ah = 


ahcdefa. 

steam admission. 






he = expansion, 
c = point of release. 
de = exhaust stroke. 




• 


ef = compression. 

■tr 






A 


^ B 






« 


cT 


-^\ 




D 


f 


v« ,1,2? a 


=^ 


OY = Pressure Axis 
OX = Yolume Axis 







' 




X 


O 


f 








'i 


P 1 = Steam Line Pressure 
' 2 = Condenser or Exhaust 

Fig. 9. 


Line Pressure 



Rankine cycle with complete expansion (also called Clausius cycle) = 
ABCD. 

Where AB = steam admission. 

BC = complete adiabatic expansion down to condenser 

pressure, 
CD = exhaust stroke, 
DA = a constant-volume pressure rise. 

The thermodynamic efficiency of the Rankine cycle (Er) is the ratio 
of the heat changed into work per pound of steam if expanded adia- 
batically (Hi — H^) to the heat necessary to raise feed water from the 
temperature of exhaust to the temperature in the boiler and evaporate it 

(Hi - q^) or Er = ^^^ _ ^^ where 

Hi = total heat per pound of steam at pressure pi. 

H2 = total heat per pound of steam at pressure p2 after adiabatic 

expansion from pressure pi. 
§2 = heat of the liquid at pressure pz. 

The thermal efficiency of an actual steam engine (Ea) may be 
expressed as the ratio of the heat actually delivered as work per pound 



THE STEAM ENGINE 27 

of steam to the heat supphed per pound, measured above the heat of the 
liquid at the exhaust pressure. The heat equivalent of 1 hp.-hr. is 

2 545 
2,545 B.t.u. Then ^^ is the heat equivalent of the useful work ob- 
tained per pound of steam, W being the pounds of steam supplied 

2 545 

per horsepower-hour. Therefore, the thermal efficiency = tt7(tI _ — \- 

Efficiency ratio is a term expressing the ratio between the thermal 
efficiency of the actual engine and the thermodynamic efficiency of the 
ideal engine operating on the Rankine cycle with complete expansion 
between the same pressure limits. Its value will then be the ratio of 
Ea to Er, or 

Efl&ciency ratio = -^ 

_ 2,545 _ Hi - H2 
" W{Hi - ^2) ' Hi-q2 

_ 2,545 
" W{Hi - H2) 

Example. — Determine (a) the thermal efficiency, (6) the Rankine 
cycle efficiency, and (c) the efficiency ratio of a condensing engine 
operating with an economy of 13 lb. of dry saturated steam per horse- 
power-hour, initial pressure 140 lb. absolute, exhaust pressure 2 lb. 
absolute. 

(a) ^1 = 1,192.2 (from steam tables). 
^2 = 94.0 (from steam tables). 

Thermal efficiency = iq/i in'o 9 _ qa\ "^ i oqq o ^ 0-178 = 17.8 per cent. 

(6) Hi = 1,192.2 (from steam tables). 

H2 = 914 (by use of total heat — entropy or ''Mollier" diagram). 
q2 = 94 (from steam tables). 

1 192 2 914 278 2 

Efficiency of Rankine cycle = i^ no o — Q4 ^ i aqq o "^ 0.253 = 25.3 

per cent. 

^ ^ T^ff; • .• 2,545 195.8 . ... 

(c) Efficiency ratio = 13(1^192.2 - 914) = 278:2 = ^'^^^ 

, , (a) 0.178 ^^^^ 

or from above = Tf^ = q ocy = 0.695. 

Condensing and Non-condensing Engines. — 

Advantages of the Condensing Type. 

1. With cylinder of given area, stroke, and piston speed the 
net effective pressure is greater than in non-condensing engines. 



28 



ENGINEERING OF POWER PLANTS 









« 


&t^.JH| 


Hi 










r-/ 




>>-'^^5i| 


'iMi. ' jh^hh 


^^^m^^gg 


u^^mi^mmm^^^ 




1 J 


K''^^'-"'-' * ^j^ 




^H 


um 


■■ 




'^m 




^ 


R 


H 




l^^k 


S 




(4 


1 


1 


li 



Fig. 10. — 24 and 38 X 48 cross-compound engine Allis- Chalmers Co. 




Fig. 11. — Section of high-speed compound engine. 



THE STEAM ENGINE 



29 



2. Another way of putting it is, same power can be secured 
by a smaller cylinder with the condensing type. 

3. Less volume of steam drawn from boiler per stroke, there- 
fore less coal required per horsepower-hour. 

4. Due to more complete expansion the condensing engine 
utilizes the heat imparted to the steam by the fuel more per- 
fectly than the non-condensing. 

5. Efficiency. T2 might be brought to about 60T., the 
ordinary temperature of the cooling water, but it is not often 
convenient to use so much water, or the cost is prohibitive; 




Fig. 12. — Armington & Sims tandem compound high-speed engine. 

consequently the temperature is usually about 100° to 130°F. 

In non-condensing plant, T2 will be 212°F. or over. Hence the 

efficiency for the condensing engine is greater. 

6. In condensing engines the heat of the condensate can be returned 

to the boiler thus saving fuel and preventing heat strains in the boiler. 



Disadvantages of the Condensing Type. — 

1. Low final temperature increases condensation in cylinder 
thereby reducing economy. 



30 



ENGINEERING OF POWER PLANTS 



2. Vacuum must be maintained. Engine must do work to 
accomplish this. Usually circulating water must also be handled. 

3. Oil in condensed steam troublesome. Often has to be 
removed to prevent boiler troubles and clogging of passages. 

4. Cannot be used where circulating water is expensive. 




Fig. 13. — Section of una-flow engine cylinder. 

Una-flow Engines, — An attempt has been made to combine the 
advantages of the single-acting engine with those of the double-acting 
engine by Professor Stumpf , whose una-flow engine is a first-class example 
of good theory coupled with clever design. The cyhnder of this engine 
is practically twice as long as the ordinary engine cyhnder, and the 
depth of the piston is the stroke of the piston minus the width of the 



Bo/'/er Pressure 



Boiler Pressure 




Fig. 14. 



Absolute ■ Vacuum Absolute Vacuum 

-Indicator cards from non-condensing and condensing una-flow engines. 



exhaust ports which are located circumferentially around the center 
line of the travel of the piston. The admission valves are double-beat 
poppet valves, located in the cylinder heads. By this construction 
many of the disadvantages of the double-acting engine are overcome 
and the good results of the single-acting cylinder are also obtained. 
Another result of this construction, the ability to carry out the expansion 
very much further is an advantage of this design. It is possible to 
expand the steam as fully and as economically in one of these cylinders 



THE STEAM ENGINE 



31 



as in the two cylinders of the ordinary compound engine.^ As the 
steam upon exhausting does not come into contact with the admission 
ports relatively high-cylinder wall temperatures are maintained at the 
admission ends of the cylinder, thus materially reducing cylinder con- 
densation. High superheats and high vacuums can be readily taken care 
of and guarantees as low as 8.8 lb. of steam per indicated horsepower- 
hour -have been made by German builders. 




Fig. 15. — Tandem compound Corliss engine. 

Compound and Multiple -expansion Engines. — 

Advantages, — 

1. High expansion and greater difference between initial and 
final temperature in steam is secured with admission through a 
longer portion of stroke. Also more favorable crank angles. 

2. Greater expansion means higher possible boiler pressure. 

3. Strain on mechanism less by receiving high pressure on 
smaller piston area. 

4. More advantageous arrangement for admitting and cutting 
off steam. 

5. Any leakage past valves in high-pressure cylinder goes to 
low-pressure cylinder and not to waste. 

6. Condensation in high-pressure cylinder evaporates and 
does work in low. . 

^ Full details and tests of this construction may be found in Prof. Stumpf's 
book, "The Una-flow Steam Engine," published by the D. Van Nostrand Co., New 
York. 



32 • ENGINEERING OF POWER PLANTS 

7. When so arranged that the several engines have independ- 
ent crankpins there is an advantage both in size of pin and in 
crank effort. 

8. With cranks quartering or at the proper angles turning 
effort is equalized thus diminishing weight of flywheel. 

9. With reheat er the quality of steam may be improved 
during expansion. 

10. Hottest steam in smallest cylinder, thus reducing loss. 

11. Range of temperature between initial and final states of 
each cylinder is less than it would be if expansion were in one 
cylinder only. 

Disadvantages. — 

1. Cost of cylinders, other than low. 

2. Additional weight and bulk. 

3. Friction loss of extra cylinder and valve-chest. 

4. Difficulties in governing. 

5. Danger of water in low-pressure cylinder, especially trouble- 
some in locomotives. 

Throttling and Cut-off Engines. — 

Advantages of Throttling. — 

1. Engine cheap to build and buy. 

2. Steam pressure exerted through considerable portion of 
stroke, hence less inequality in steam effort at beginning and end 
of stroke. 

3. Throttling effect has a tendency to dry out moisture in 
steam and to diminish moisture in cylinder. 

Disadvantages of Throttling. — ■ 

1. Not as sensitive as cut-off engine to instantaneous varia- 
tion in the resistance. 

2. Does not regulate as closely to speed as cut-off type. 

3. Exhaust usually at higher pressure than in cut-off, causing 
rejection of more heat. 

Advantages of Cut-off Engine. — 

1. Effort controlled per stroke of engine. 

2. Engine sensitive immediately to variations in resistance. 

3. More certain to be kept at uniform speed by governor. 

4. Full boiler pressure exerted on piston until cut-off. 

5. Full advantage from expansive working. 



THE STEAM ENGINE 



33 



Disadvantages. — 

1. Wide difference of effort at two ends of stroke requiring 
massive flywheel. 

2. Design and complication of valve-gear. 

3. Engine costly to build and buy. 

4. Cylinder condensation increased by lower terminal pressure 
and temperatures. 

For many classes of work in power-house service variations are so 
wide that automatic cut-off is essential. Where effort is constant, as 




Fig. 16. — Nordberg four-cylinder steam hoisting engine. Calumet & Arizona 

Mining Co. 

in pumping, in railway and in marine practice, throttling is close enough, 
especially when the engine driver has to be in constant attendance. The 
automatic cut-off is usually more economical, and the engine is usually 
better built." When desirable to cut off later than one-third stroke there 
is little gain in carrying boiler pressure much higher than 80 lb. gage. 
For simple engines the steam pressure is seldom above 80 lb. gage, but 
for compound it ranges from 80 to 250 lb. 



34 



ENGINEERING OF POWER PLANTS 




Fig. .17.— Manhattan type duplex cross-compound engine. Subway Power 

House, New York. 



Triple- and quadruple-expansion engines are used little save for 
pumping and for marine work. The steam pressure for these engines 
usually runs from 125 to 250 lb. 

Special Classification. — 1st. Stationary; 2d Traction; Sd Marine. — 

The first is subdivided into: 

(a) Factory or mill, including power-house; 

(6) Pumping engines, including blowing engines and air compressorh,' 

(c) Hoisting engines; 

(d) Locomobiles; 

(e) Miscellaneous engines. 

The second is subdivided into: 

(o) Locomotives, traction engines, including road-rollers and self-propelled steam 
fire engines, auto trucks and automobiles and agricultural engines. 

The third consists of engines for marine service. 



THE STEAM ENGINE 35 

Engine Flywheels. — -Flywheels are necessary in the majority of in- 
stallations. Marine engines require no flywheels, or rather the water- 
wheel and propeller serve this purpose. The locomotive requires no 
flywheels since the driving wheels and the living force of the engine and 
train serve this purpose. When there are two cranks at 90°, or three at 
120°, the weight of the flywheel diminishes rapidly. For rough work in 
rolling mills, etc., with quartering cranks the flywheel is often dispensed 
with to facilitate quick reversal of the engine. 

The size of the wheel depends upon the regulation required of a given 
engine. A variation of 5 per cent, in the speed is often allowable in 
factory engines while in certain types of electric lighting stations the 
allowable variation is only 1 per cent. On large, important 60-cycle 
installations a variation either side of perfect rotation of one-fourth of a 
geometrical degree has been specified. 

A fair guarantee to ask is that the speed of the engine shall not vary 
more than from 2 to 2)-^ per cent, above or below the normal speed 
under any conditions of load. 



Fig. 18. — Nordberg poppet-valve engine, tandem compound. 

Rotary Steam Engines. — 

Advantages, — 

1. Effort of steam applied directly to produce rotary motion. 

2. No reciprocating parts, therefore no inertia effects. 

3. No dead centers. 

4. Absence of reciprocating parts makes it easy to run at 
high speed. 

5. Very compact. Occupies little room. 

6. Either no valve gearing, or very simple if any. 

7. Cheap to build. Should be cheap to buy. 

8. No reciprocating rods or dead centers, hence condensed 
steam in cylinder does no harm. 

9. Increased construction and item 8 adapt it to outdoor 
service. 

10. No skill required to handle it. 



36 



ENGINEERING OF POWER PLANTS 



Disadvantages . — 

1. Difficulty of satisfactorily packing surfaces which do not 
move through equal spaces in equal times. 

2. Expense connected with proper lubrication. If efficiently 
lubricated they consume an excessive amount of oil. 

3. Excessive waste space to be ffiled with steam each revolu- 
tion. 

4. In simple type, non-expansive. This coupled with items 
1 and 2 make it uneconomical. 




Fig. 19. — Section of Herrick rotary engine. 



5. Difficult to design for large horsepowers. Structure 
becomes inconvenient the moment large areas are desired in 
order to make P X A large. Difficult to secure high-piston 
speed in feet per minute without making the engine excessively 
large. 

Economy may be secured by arranging in series upon a shaft, so that 
the steam rejected from No. 1 drives No. 2 of larger volume. Few if 
any rotary engines have been commercially successful. In view of this 
fact it may be well to record the general data for a rotary engine tested 
by one of the authors. 



THE STEAM ENGINE 



37 




1=4=3 



38 



ENGINEERING OF POWER PLANTS 




Fig. 22. — Oscillating marine steam engine, section, through air pump. 



THE STEAM ENGINE 39 

1. The simple steam motor of 20-b.hp. rating occupied only approxi- 
mately 12 cu. ft. of space overall. 

2. The motor which was under load for 5 hr. continuously showed no 
indications of heating or variations in uniformity of action. Its speed 
regulation for varying loads was remarkable. 

3. The steam consumption of this unit was exceptional, clearly sur^ 
passing the corresponding consumption of the average reciprocating unit 
of similar capacity. 

4. After one year of service this rotary engine showed an increased 
steam consumption per brake horsepower-hour of only 4.6 per cent. 



STEAM TURBINES 

Basic Principles. — The steam turbine, like the water turbine, utilizes 
the kinetic energy of fluid in motion. Whenever a moving fluid impinges 
on moving vanes which change the direction of flow and reduce the 
velocity of the fluid, the energy of the fluid is converted into mechanical 
work and is available through the shaft on which the moving vanes are 
placed. 

Differences between Steam and Water Turbines. — There are two 
important distinctions between steam and water turbines. First, pro- 
vision must be made in the steam turbine for converting the heat energy 
of the steam into kinetic energy or the energy of motion. To accomplish 
this the steam turbine is furnished with nozzles so designed as to control 
the expansion of the steam in a way to augment its velocity. These 
nozzles are of two types, diverging and converging. Where the drop 
of pressure is large the diverging nozzle is used. In this nozzle the 
walls diverge in the direction of the flow of the steam, so that its outlet 
area is larger than its inlet area. Where the drop of pressure is smaller 
the converging nozzle is used. These nozzles differ from the nozzle of 
the water turbine in that they perform two functions, they not only 
direct the flow of steam, but they assist in the necessary expansion re- 
quired to convert the heat energy into kinetic energy. In the Parsons 
type the fixed blades form a series of nozzles. Second, although jet 
velocities higher than 300 ft. per second are common on the Pacific 
Coast, in water turbines the ordinary water velocities are well below this 
figure. In the steam turbine the velocities are very much greater and 
the turbine must be adapted to velocities as high as 3,000 to 4,000 ft. 
per second. It is interesting to compare this speed with the muzzle 
velocity of a modern rifle ball, which leaves the barrel at about 2,600 
ft. per second, or in the neighborhood of 30 miles per minute. This is 



40 ENGINEERING OF POWER PLANTS 

the speed of steam discharging into the atmosphere from a nozzle of the 
best shape under a pressure of 50 lb. gage. 
In the successful steam turbine: 

1. As much of the heat energy of the steam as possible must be converted into 
kinetic energy. 

2. The rotor, nozzles and guide passages must be capable of utilizing the kinetic 
energy of the steam in the most efficient manner. 

3. The casing, rotor and blading must hold their form under the heat strains and 
centrifugal strains and must be tight against leakage. 

4. The apparatus must run at the proper speed at the point of delivery of power 
and all parts must run within safe limits. 

Comparison with the Steam Engine. — In the steam turbine the 
process of expansion of the steam as in the steam engine is duplicated, 
except that the flow of steam is continuous instead of intermittent. 
The steam engine may be termed a ratchet mechanism, while the steam 
turbine is a continuous mechanism. The difference in form of the turbine 
and engine is due to the fact that the turbine is designed to work by 
changing the direction of motion of the flowing steam, while the engine 
is designed to operate by the direct pressure of the steam. The turbine 
is thus a velocity motor and the steam engine a pressure motor. 

Impulse and Reaction Turbines. — In an impulse turbine the wheel is 
moved by the impulse of a jet of steam impinging on the blade surfaces. 
In the true reaction turbine the jet of steam issues from the moving part 
and impinges on the atmosphere or a fixed blade, thus moving the rotor 
by ifeaction. These terms are not used in this way at the present time 
and the distinction usually made is that in the impulse wheel the expan- 
sion of the steam is complete within the nozzle, while in the reaction wheel 
the expansion is not completed until after the steam enters the moving 
bucket. These terms are not good terms to use to distinguish the 
different types of turbines. Another way of stating this difference is 
that impulse turbines are partial-entry or ventilated turbines, while 
reaction turbines are full-entry or drowned turbines. It is better not 
to use these terms. 

-Classification of Turbines. — Turbines may be classified first as to 
size into small turbines and large turbines, the small turbine being 
built in sizes up to 750 hp. or 500 kw., the large turbine, commencing at 
this size and going up to the limit of mechanical construction, which at 
the present time may be from 30,000 to 60,000 kw. or larger. Large 
turbines are usually classified by the names of their inventors or manu- 
facturers and the following types may be distinguished: Parsons, 
Curtis, Rateau, Zoelly and composite. All of these turbines are very 
much alike in principle, but differ widely in mechanical design and 
construction. 



THE STEAM ENGINE 



41 



The Parsons turbine was the first of the large turbines to be successful 
and is now manufactured in both Europe and America. The con- 
struction is of the drum type in which the blades are fixed in grooves on 
the outside of a cylindrical drum for the rotor, the fixed blades being 
held in grooves on the inside of the casing All Parsons turbines are full 
intake machines and require for complete expansion from 200 lb. steam 
pressure down to 28 in. of vacuum, about 80 rows of blades, 40 fixed and 
40 moving. No glands are necessary to prevent leakage between the 
stages, as the pressure differences are quite small, and the clearances at 
the end of the blades very small indeed. Each manufacturer of Parsons 
turbines varies the design in minor details, such as thrust bearing, loca- 




FiG. 23. — 35,000 K.W. Westinghouse turbo-generator unit at North West Station, 

Chicago, 111. 

tion of dummies, type of blading and mechanical construction of the 
drum and casing. 

The Rateau turbine is of the partial-entrance type and so-called 
multi-cellular construction. The drum system of construction is rarely 
used, the guide blades are held in diaphragms with glands to prevent 
leakage where the shaft passes through them. About 20 stages are 
usually used for the range of expansion between 200 lb. pressure and 
28-in. vacuum. 

The Zoelly turbine is of the full intake type, but closely follows the 
Rateau construction in general lines with the exception that more cast 
iron and cast steel are used in its construction and considerably less 
riveted-steel work. In this turbine it is very rare that more than 12 
stages are used for the expansion of steam from 200 lb. to 28-in. vacuum. 

The Curtis turbine, which originated in America^ has been classed 



42 



ENGINEERING OF POWER PLANTS 



as the multiple-velocity stage type. It is always partial intake and from 
three to six stages are necessary for the expansion from 200 lb. to 28-in. 
vacuum. The particular feature of this type is that in- each stage two 
or more velocity stages may be used. The construction is somewhat 
similar to the Zoelly machine, with the exception that the shaft has been 
placed in a vertical position and held by a step bearing. The clearances 
in this machine can be very generous, as they are in the Zoelly and Rateau 
types. The diaphragms between the stages are provided with a gland 
where the shaft passes through them, thus preventing leakage from 
stage to stage. 




Fig. 24. — 7000-kw., 1800-r.p.m., Curtis steam turbine. 

The Parsons, Zoelly, and Rateau constructions seem to give much 
better results in that part of the expansion between atmosphere and 
28 in. of vacuum. The Curtis and Rateau types appear to give a 
trifle better result in the part of the expansion between 200 lb. and 
atmosphere. When these facts became known some manufacturers 
started building what we have termed the composite type of machine 
by using a Curtis wheel for the first stage and the Parsons, Zoelly, or 
Rateau machine for the low-pressure end. This construction resulted 
in a shorter, stiffer and cheaper machine and the economies obtained 
were extremely good. Shortening the machine and decreasing the 
number of stages enabled the manufacturers to build machines of a 
size much larger than the old construction, and the simplified wheel 
constructions enabled higher speeds to be used with the attending 
economies. Any combination of the various type machines may be 



THE STEAM ENGINE 



43 



made and at the present time practically every turbine manufacturer 
is turning out the composite machine as the bulk of his product, although 
machines of the straight Parsons, Zoelly and Curtis type are being 
built. 



^—Single Flow 
Reaction Element 

Reaction Element. 



fxhaust -'^^ 



Impulse Wheel 

' Dummy 
-Reaction Element 




Fig. 25.- 



Exhcust 



Nozzle Chamber 

■Section of a Westinghouse semi-double-flow turbine. 



It should be noted that the governing of all full intake machines is 
of the throttling or puff type, while the governing of the partial intake 
machines is almost entirely of the nozzle type, that is the steam is 



^SV^■^.SV^.^.^,^.........;^ 




Vr^P^^?^ 



Fig. 26. — Brown, Bouverie & Co. composite-type turbine. 

admitted at full pressure to one or more nozzles, depending on the load 
on the turbine. 

Quite recently in Sweden the Ljungstrom turbine has been placed 
on the market, which differs materially from the other types of large 
turbines. The Ljungstrom turbine is a radial-flow machine, in which 
the steam is admitted through the center of the shaft and passes through 
the blades in a radial direction to the condenser. There are no fixed 
blades, but two sets of working blades moving in opposite directions. 
By this means bucket speeds may be kept high with reasonable low 
shaft revolutions. Tests of this machine are extremely good and if 



44 



ENGINEERING OF POWER PLANTS 



1 'I 






:ni 




W0m^ 



• <««»!* -««»» "«<«»- -^fcl*--'^^ 



Fig. 27. — 1400 kw. Ljungstrom turbine and condenser, Sandriken, Sweden. 




Fig. 28. — Bergmann (Curtis-Rateau) composite type turbine. 



THE STEAM ENGINE 



45 



the blade construction, which at first sight appears very flimsy, bears the 
test of time, it may be classed as a fifth-basic type of turbine. 

Small Turbines. — Small turbines are of many types, but may be 
classified by the method in which the steam is used in the wheel. In 
the DeLaval the steam is expanded in a nozzle and is passed once through 
the buckets of a single wheel. This was the first successful turbine and 
has been used to a great extent. This naturally leads to high bucket 
speeds and in the small sizes to a very high speed of rotation, in some 
cases as high as 12,000 revolutions per minute. In order to make the 
turbine a usable proposition a special reduction gearing was made for 
reducing this speed to the proper point. 

In the small turbine of the Curtis manufacture the wheel is provided 




Fig. 29. — Zoelly steam turbine. 



with two or more sets of blades and the steam is used a number of times 
on the same wheel, each velocity stage using a portion of the jet velocity. 

In the Riedler-Stumpf turbine the nozzle has a number of return 
passages behind it returning the steam to the wheel buckets. 

In the Terry type the nozzle carries behind it a number of ventilated- 
return passages, by which the steam after passing through the wheel is 
returned two or three times to the wheel buckets on the entrance side. 

In the Electra or Westinghouse type, the steam having passed once 
through the buckets of the wheel, is caught by a return passage, which 
returns the steam to the wheel on the discharge side and passes it through 
the buckets in a contrary direction. 



46 



ENGINEERING OF POWER PLANTS 



In the Kerr type the buckets are almost exactly similar to those of 
the Pelton waterwheel and the steam is used only once in a set of buckets. 
This necessitates a number of stages when economy is to be secured. 

Most of these turbines, when built in the larger sizes, have more 
than one wheel and as they increase in size, approach in construction 
some one of the large turbine types. 

By far the largest use for the small steam turbine is for auxiliary work 
and they are largely run non-condensing. In this case the economy is 
not quite so good as that of a good steam engine when kept in good con- 
dition, the • difference being that with the engine the economy will not 
hold up, whereas with the turbine there is no falling off of steam economy 
with age and wear. The larger sizes are almost always run condensing, 
giving economies not quite so good as those of a first-class steam engine 
under the same conditions. 




Fig. 30. — Section of Kerr turbine. 



Low-pressure or Exhaust, Bleeder and Mixed-pressure Turbines. — 

Since that portion of the turbine which utihzes the expansion of the 
steam from around atmospheric pressure to the best obtainable vacuum 
is much more efficient than the high-pressure portion of the turbine, it 
was proposed very early in the turbine development to install low- 
pressure or exhaust turbines in connection with non-condensing engines 



THE STEAM ENGINE 47 

already installed. The combination unit gave nearly double the power 
of the engine unit alone, was somewhat less costly per unit capacity and 
resulted in a saving of from 5 to 10 per cent, or even more in operating 
costs. These savings were particularly large in connection with the 
exhaust from rolling mill, hoisting and reversing engines and steam 
hammers, but as these machines were of intermittent service some 
method of providing steam during the period of rest had to be intro- 
duced. This led Professor Rateau, one of the earliest to use this type of 
machine, to invent his regenerator, which provided storage to tide over 
the intermittent periods of stopping. Other manufacturers got around 
the difficulty in another way by the introduction of an auxiliary Curtis 
high-pressure wheel ahead of the low-pressure element and providing a 
governor valve which admitted high-pressure steam to run the turbines 
during the periods when no low-pressure steam, or not enough, was 
available. These machines are known as mixed-pressure turbines and 
have become quite common, as they are well suited to certain conditions. 
The Rateau regenerator practically consists of a large cast-iron tank 
acting as a jet condenser at atmospheric pressure. A slight reduction 
in the pressure vaporizes some of the stored water, thus providing steam 
for the low-pressure turbine. Combinations of regenerator and mixed- 
pressure turbines are also used with good success. (For the theory of 
regenerators, see paper by F. G. Gasche, Engineers' Society of Western 
Pennsylvania, Nov. 19, 1912.) 

It is sometimes convenient, especially in district Hghting and heating 
systems, to abstract steam from the turbine at a little above atmospheric 
pressure, this steam to be used in the heating system or for similar uses. 
Such a turbine is known as a bleeder turbine. The steam is taken off 
through a specially designed valve arranged to maintain any predeter- 
mined pressure in the bleeder main. 

By combining^ the superior efficiency of the engine in the pressure 
range above the atmosphere with that of the turbine below the atmos- 
pheric range a resultant superior to the efficiency of either single type 
may be secured. Standard piston engines are able to sustain full rated 
load when run non-condensing and often will carry from 25 to 50 per 
cent, above rated load without danger of excessive wear. Under such 
conditions the water rate per kilowatt-hour is high but all the heat 
rejected in the exhaust is available to a low-pressure turbine; hence the 
net economy of the combined engine and turbine may be considerably 
superior to that of the engine when run condensing. By proportioning 
the turbine to efficiently utilize the exhaust steam and by connecting 
to it a high-vacuum condenser, the initial capacity of the unit may be 
doubled or even trebled, and if the engine is in good condition, the 

^"American Handbook for Electrical Engineers," p. 1395. 



48 ENGINEERING OF POWER PLANTS 

resultant efficiency may be superior to that obtainable from a new 
complete-expansion turbine of equal capacity. 

Combined Engine and Turbine Unit. — Owners of first-class recipro- 
cating steam-engine plants will often be confronted with the desirability 
of the extension of their plants. This may be done in a number of 
ways, by the duplication of the engine units, by the purchase of complete 
expansion turbines, or by installing low-pressure turbines, to operate 
on the exhaust steam from the existing steam engines. It is difficult 
to say which of these ways is the best, as the local condition will largely 
govern the problem, but it is safe to say that in no case at the present 
time in plants of 1,000 hp. or larger, will the reciprocating engine plant 
be duplicated. In a few cases it has been found advisable to install 
low-pressure turbines, but in most instances complete expansion turbines, 
replacing the original engines, will be the most economical solution. 
Each case, however, should be considered by itself, bearing in mind 
that the cost of the low-pressure steam turbine will be about two-thirds 
of that of a complete expansion turbine capable of developing the power 
of the engine and low-pressure turbine combined. 

Rating of Steam Turbines. — Turbine ratings are usually based on 
maximum sustained load. Momentary overload capacity is very large 
and moderate overloads of considerable duration can be carried but may 
require the admission of high-pressure steam to low-pressure stages 
by means of a secondary valve. Small turbines for driving pumps, 
blowers, etc., are rated in horsepower. Turbines used to drive electric 
generators are usually rated in connection with the generator, the 
combined unit or turbo-generator being rated in kilowatts. 

Efficiency and Losses.^ — The maximum theoretical efficiency of a 
steam turbine is the efficiency of the Rankine ideal engine between the 
temperatures of admission and exhaust. 

The several losses which tend to reduce the efficiency of turbines below 
the theoretical maximum are (1) residual velocity, or the kinetic energy 
due to the velocity of the steam escaping from the turbine; (2) friction 
and imperfect expansion in the nozzles; (3) windage, or friction due to 
rotation of the wheel in steam; (4) friction of the steam traveling through 
the blades; (5) shocks, impacts, eddies, etc., due to imperfect shape or 
roughness of blades; (6) leakage around the ends of the blades or through 
clearance spaces; (7) shaft friction; (8) radiation. The sum of all these 
losses amounts to about 25 per cent, of the available energy in the largest 

* "American Handbook for Electrical Engineers," p. 1399. 

Note. — For a review of present turbine construction practice, see paper by Prof. 
A. G. Christie, vol. 34, A.S.M.E. Transactions, p. 435 Vol. 31 of the same Trans- 
actions contains a paper by one of the authors which gives sections and steam-con- 
sumption curves of most of the types of small turbines. 



THE STEAM ENGINE 49 

and best designs and to 50 per cent, or more in small sizes or 
poor designs. 

Oil Required by Steam Turbines. — No cylinder oil is required for 
the turbine and the exhaust may be condensed and used over and over 
again as feed water for the boilers without danger, providing exhausts 
from oily condenser auxiliaries are not permitted to mix with the con- 
densed steam. The only oil required by the turbine is the medium 
machine oil used for the turbine bearing. This oil is small in quantity, 
since the bearings of small machines are ring oiled and require to be 
filled up only about once per month. All large machines have a forced 
lubrication system for the bearings with a filter and pump attached to 
the turbine and the oil is used over and over again. 

Noise, — The earlier turbo-generators were very noisy, due to the fan 
action of the rotor. Modern design encloses the stator and the forced 
ventilation, provided by the fan action of the rotor or an outside blower 
reduces this noise to a reasonable amount. Where, however, a number 
of large generators are ventilated from one duct it is well to make pro- 
visions for a dampening action and to take particular precautions that 
an organ-pipe effect is not produced. A great deal of attention has been 
given to the reduction of noise in turbo-generators, and while it is not 
possible to entirely eliminate it, the noise has been reduced to a reasonable 
amount. 

Efficiency, Economy and Cost of Steam Engines and Steam Turbines. 
The mechanical efficiency of the same engine will often vary consider- 
ably from time to time, depending upon the operating conditions. In 
general the mechanical efficiency of various types of engines varies from 
0.80 to 0.94, although better figures have been secured under test and 
poorer results are frequently encountered in practice. 

The following table gives a few efficiencies secured from tests of engines 
under normal but good working conditions. The influences of work- 
manship in the construction of the engine and the variation in operating 
conditions are apparent from the variation in efficiencies shown. 



50 



ENGINEERING OF POWER PLANTS 



Kind of engine 



Horsepower 


Efficiency 


25 


0.86 


80 


0.91 


50 


0.92 


100 


0.90 


150 


0.85 


100 


0.86 


80 


0.88 


75 


0.90 


300 


0.86 


100 


0.90 


46 


0.87 


650 


0.93 


6,000 


0.97 


800 


0.94 to 0.97 



Simple engines: 

Horizontal portable 

Horizontal portable 

High-speed, stationary. 

High-speed, stationary. 

Corliss, condensing 

Corliss, non-condensing 

Compound:. 

Portable 

Horizontal, stationary 

Horizontal, mill engine 

Corliss, condensing 

High-speed, condensing 

Pumping engine 

Vertical three-cylinder compound electric-lighting 

engine. . „ 

Triple-expansion : 

Vertical pumping engines 



The following results, secured from three triple-expansion pumping 
engines under test at St. Louis, indicate the possibilities under condi- 
tions of superior workmanship and exceptionally refined conditions of 
operation. 



No. 1 


No. 2 


No. 


3 


I.hp. 


Eff. 


I.hp. 


Eff. 


I.hp. 


Eff. 


873 


96.6 


875 


96.8 


859 


97.7 



Although, strictly speaking, there is no relation between the horse- 
power capacity of engines and mechanical efficiency, a small engine often 
being more efficient than a large one, yet in general it is probably true that 
considering workmanship as a whole, the number of cheap engines of 
relatively small size and the greater skill and care usually exercised in the 
operation of large units, a sufficiently close relation between mechanical 
efficiency and size may be assumed to warrant the use of the following 
tables of approximate mechanical efficiencies for reciprocating steam 
engines. 



THE STEAM ENGINE 



51 



Mechanical efficiency of reciprocating steam 
engines^ rated load 


Mechanical efficiency of steam engines in per 
cent, of rated load efficiency 


I.hp. 


Efficiency, per cent. 


Per cent, of rated load 


Per cent, of rated load 
efficiency 


5 


80.0 


100 


100.0 


25 


83.5 


90 


99.0 


5Q 


85.0 


80 


97.2 


200 


86.5 


70 


95.2 


400 


89.0 


60 


92.5 


500 


90.0 


50 


89.0 


1,000 


90.8 


40 


83.4 


,2,000 


92.5 


30 


74.0 


3,000 


94.0 







Steam-engine Economy. — F. W. Dean says^ in speaking of the 
economy of steam plants: 

"It is well known that the economics of such plants are very variable and differ 
from each other In some cases great care is taken to have good plants carefully 
operated, while in others they are neglected and incompetent men are employed." 

He further says: 

*'In the case of engines there are non-condensing and condensing engines and 
turbines, and they can be simple or compound. In addition there are steam 
engines that are being devised which are likely to surpass in economy any that 
are now on the market, and these improved engines are on the verge of being 
introduced (December, 1914). In addition superheated steam is being intro- 
duced. By its use it is easy to save 10 per cent, of coal without any accompanying 
disadvantages. The advantage of using better condensing apparatus is being 
realized and such apparatus is being introduced with improved economy." 

As emphasized in specifications for economy in the use of the steam: 

"After the steam has been delivered to the engine, care should be taken to 
see that it is utilized to best advantage. When all the steam is needed, the eco- 
nomy or rate of the engine itself is not of particular consequence; that is, a simple 
slide-valve engine using steam at the rate of 40 or 50 lb. per horsepower hour 
may be the most desirable type to use. As the demand for exhaust steam 
decreases, the importance of economy in the engine increases. Should there be 
periods during which all of the exhaust is not used, the maximum economy of 
the engine during these periods is of utmost importance. At such times the most 
economical generating unit should be selected and one of a size that will be 
economically loaded with the amount of power developed." 

Average Steam Consumption of Reciprocating Steam Engines. — 
Although the range of steam consumption per horsepower per hour is 
wide for engines of a given size and of different types, depending upon 
the quality of construction and the degree of refinement called for by 
commercial demands^ an idea of the average economy of reciprocating 
steam engines may be had from the following table, 

1 A.S.M.E. Transactions, vol. 36, p. 839. 



52 ENGINEERING OF POWER PLANTS 

Pounds of Dry Steam per Indicated Horsepower-hour op Full Rated Load 





Simple high-speed 


Simple low-speed 


Compound high-speed 


Compound low-speed 


Lhp. 


Non-con- 
densing 


Con- 
densing 


Non-con- 
densing 


Condens- 
ing 


Non-con- 
densing 


Condens- 
ing 


Non-con- 
densing 


Condens- 
ing 


10 


65.0 


50.0 














15 


57.0 


44.0 














20 


52.5 


40.0 














25 


49.0 


38.0 














30 


46.5 


36.0 














40 


42.5 


33.0 














50 


40.0 


30.2 














60 


38.0 


28.5 














75 


35.5 


26.2 














100 


33.0 


23.4 


27.0 


21.6 


29.3 


22.5 


23.6 


20.0 


150 


30.4 


21.5 


26.3 


21.0 


28.6 


22.0 


23.1 


19.5 


200 


29,5 


20.6 


25.7 


20.5 


27.9 


21.5 


22.7 


19.0 


250 


29.0 


20.2 


25.2 


20.0 


27.3 


21.0 


22.3 


18.5 


300 


28.5 


20.0 


24.8 


19.6 


26.6 


20.5 


21.9 


18.1 


400 






24.1 


18.8 


25.4 


19.5 


21.1 


17.3 


500 






23.7 


18.3 


24.2 


18.6 


20.4 


16.5 


600 






23.4 


17.9 


23.3 


17.9 


19.8 


15.8 


700 






23.2 


17.7 


22.7 


17.5 


19.2 


15.3 


800 






23.0 


17.6 


22.3 


17.2 


18.7 , 


15.0 


900 






22.9 


17.5 


22.1 


17.0 


18.4 


14.7 


1,000 






22.8 


17.4 


22.0 


16.9 


18.2 


14.5 


1,500 
















13.8 


2,000 
















13.5 


2,500 
















13.2 


5,000 
















12.5 



Probable Gain in Steam Consumption by Condensing. — The follow- 
ing table serves to illustrate the marked gain in steam consumption of 
condensing engines over non-condensing. The figures given are approxi- 
mations only. 

Pounds Dry Steam per Indicated Horsepower-hour 



Type of engine 



Non-condensing 



Probable 
limits 



Assumed 
for com- 
parison 



Condensing 



Probable 
limits 



Assumed 
for com- 
parison 



Per cent, 
gained by 
condens- 
ing 



Simple high-speed 
Simple low-speed . 
Comp. high-speed 
Comp. low-speed. 
Triple high-speed. 
Triple low-speed. . 



65-25 
30-22 
30-22 
24-18 
27-17 



33 
25 
26 
21 
22 



50-19 
24-17 
24-16 
20-12 
23-14 
18-11 



23 
19 
20 
17 
17 
16 



30 
24 
23 
19 
23 



THE STEAM ENGINE 



53 



The probable steam consumption of condensing engines of different 
types with different pressures of steam is given in a set of curves by R. 
H. Thurston and L. L. Brinsmade, Transactions A.S.M.E., 1897, from 
which curves Kent has derived the following approximate figures. 

Steam Pressure, Absolute 



Pounds per square inch 



400 



300 



250 



200 



150 



100 



75 



50 



Ideal engine (Rankine cycle) . , 
Quadruple exp. wastes 20 per 

cent 

Triple exp. wastes 25 per cent. 
Compound wastes, 33 per cent. 
Simple engine wastes, 50 per 

cent 



6.95 

8.75 

9.25 

10,50 

14.00 



7.5 

9.15 

9.95 

11.25 

15.00 



7.9 

9.75 
10.50 
11.80 

15.80 



8.45 

10.50 
11.15 
12.70 

16.80 



9.20 

11.60 
12.30 
13.90 

18.40 



10.50 

13.00 
14.00 
15.60 

20.40 



11.40 

14.00 
15.10 
16.90 

22.70 



12.90 

15.60 
16.70 
18.90 

25.20 



These engines are of the usual ratios of expansion. A 1 to 7 com- 
pound will be as economical as a 1 to 7 triple or quadruple expansion 
engine. 

It is conservative to say that compound engines may now be built 
to produce an indicated horsepower on 12.5 lb. of saturated steam per 
hour. With high degree of superheat the 10-lb. mark has been passed 
but if results were calculated on the basis of saturated steam the figures 
would barely reach 10 lb. 

From 23 four-valve engines in commercial operation, Barrus reports: 

1 falls below 12 lb. per horsepower-hour 

3 fall below 13 lb. per horsepower-hour 

16 fall below 14 lb. per horsepower-hour 

only 3 fall above 14 lb. per horsepower-hour 

The table on pages 54 and 55 gives an excellent idea of the rela- 
tive steam economy of different types of engines under test conditions. 

One of the recent developments of the reciprocating steam engine 
in this country (long used in Europe) is the Lentz compound engine which 
in many respects resembles the modern horizontal, tandem double- 
acting gas engine. 

Tests of a 143^ and 24^ bt 27)^-In. Engine 



steam pressure, 
lb., gage 


Vacuum, in., 
Hg. 


Superheat, °F. 


R.p.m. 


I.hp. 


Lb. steam peri.hp.-hr. 
under initial condi- 
tions 


170 
170 


26 

26 



150 


167 
167 


366 
366 


12.3 

10.4 



Tests have recently been reported by the manufacturers which give 
the steam consumption of a 115-hp. Buckeye-mobile, running at 248 



54 



ENGINEERING OF POWER PLANTS 






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56 



ENGINEERING OF POWER PLANTS 



r.p.m.; steam at 210 lb.; initial superheat, 171 °F.; non-condensing, as 
13.3 lb. per indicated horsepower-hour. This unit produced an in- 
dicated horsepower-hour on 1.33 lb. of coal having a calorific value of 
14,500 B.t.u. per pound. A 169-hp. unit running at 200 r.p,m.; steam 
at 209 lb.; inital superheat, 218°F.; vacuum 25.7 in., showed a water 




Fig. 31. — Compound locomobile using superheated steam and surface condensers. 

rate of 9.2 lb. per indicated horsepower-hour. The coal consumption, 
using fuel with a calorific value of 14,209 B.t.u. per pound, was 1.08 lb. 
per indicated horsepower-hour. 

The effect of superheating upon the steam consumption is brought 
out more clearly by the following test results. The consumption is 
given in pounds per horsepower-hour of superheated steam and also in 
equivalent pounds of saturated steam. 



I.hp. 


Superheat, °F. 


Lb. steam, i.hp.-hr. 


Equivalent, sat. steam 


B.t.u. per i.hp.-hr. 


222 


0.0 


12.08 


12.08 


15,000 


226 


43.7 


11.58 


11.77 


14,600 


227 


97.7 


11.00 


11.44 


14,200 


223 


151.7 


10.67 


11.33 


14,000 


223 


221.2 


9.81 


10.69 


13,300 


218 


310.9 


8.89 


10.01 


12,000 



THE STEAM ENGINE 



57 



The result shows that for every 100°F. superheat the steam con- 
sumption per indicated horsepower-hour was reduced 1 lb. or 8.5 per cent. 



= 70 

o 

^ 65 

W 60 

« 55 



a.- 40 

» 25 

'S 

^: 20 



Y 




\ 


\ 


■ i ^" 


^1 




^^■--^^ 







1000 2 3 450006 7 8 9 10000 11 12 13 14 15000 16 17 18 19 20000 
Peripheral Speed Ft./kin. 

Fig. 32. — Average water rates for small steam turbines (75-200 H. P.) with 175 lbs. 
gauge pressure, 100°F. superheat and atmospheric exhaust. 




Fig. 33. — Section of Terry steam turbine. 

and that the consumption expressed in terms of equivalent saturated 
steam was reduced 0.6 lb. per indicated horsepower-hour. It should 
be remembered that the poorer the engine the larger the gain from the 



58 



ENGINEERING OF POWER PLANTS 



use of superheat. In a first-class engine the gain in economy is rarely- 
over 5 per cent, per 100°F. superheat, but in a poor simple non-condensing 
engine it may be 50 per cent, for the first 100° superheat. 

Steam Consumption of Small Steam Turbines. — The majority of 
small steam turbines are run non-condensing and are rated on the brake 
horsepower instead of the indicated. The steam consumption for 
different-sized turbines varies with the speed. An estimate of the 
average consumption for non-condensing units may be secured from the 
following curve, Fig. 32. 

The values would be materially increased by back pressure. Esti- 
mates of the probable steam consumption of the larger condensing 
steam turbines may be made from the following tables, keeping in mind 
that the figures recorded are test results under the best operating 
conditions. 



Records 


OF Steam Consumption for Turbines 










Nominal 
power 


Steam used per hr., lb. 


Estimated 
equivalent 




B.hp. 


E.hp. 


Kw. 


i.hp. 


With saturated steam 



Westinghouse Parsons. 
Westinghouse Parsons. 

Rateau 

Curtis (American) 

DeLaval 

Zoelly 



400 kw. 
1,250 kw. 
300 hp. 
500 kw. 
300 hp. 
500 hp. 



13.63 









14.13 


18.95 





14.90 




13.63 








15.17 









16.05 


21.50 



12.68 
12.72 
13.11 
12.68 
13.96 
14.12 



With superheated steam, not exceeding 150°F. 



Parsons 

Westinghouse Parsons. 

Curtis (American) 

Parsons 

Zoelly 

Westinghouse Parsons, 

DeLaval 

Parsons 

Curtis (Enghsh) 



3,000 kw. 

400 kw. 

500 kw. 
1,500 kw. 

500 hp. 
1,250 kw. 

300 hp. 

300 kw. 

500 kw. 





11.79 


15.80 


12.07 








13.28 


17.79 





13.44 


18.00 




14.05 


18.82 




13.78 


18.48 


13.94 








14.96 


20.06 


..... 


15.29 


20.50 



With highly superheated steam, superheat from 180° to 290°F. 



Parsons 

Curtis (American) 

Curtis (American) 

Westinghouse Parsons. 



5,000 kw. 

500 kw. 
2,000 kw. 

400 kw. 





11.00 


14.74 




11.26 


15.10 




11.27 


15.12 


11.17 







10.85 
11.23 
11.95 
12.10 
12.36 
12.40 
12.82 
13.16 
13.76 



10.12 
10.14 
10.36 
10.39 



THE STEAM ENGINE 



59 



Economy Tests op Turbines (Marks and Davis Tables) 
In calculating Rankine B.t.u. an efficiency of 90 per cent, is assumed for turbine and 

generator 



Turbines 



Load, 

kw. 



Steam 
press, 
abs. 



Super- 
heat, 
°F. 



Vac. 
29.92 

in. 
Bar. 



Lb. 
steam 
per 
kw.- 
hr. 



B.t.u. 
per 
kw.- 
min. 



Rankine 
cycle, 
B.t.u. 

per kw.- 



Eff. 
ratio 



Dunstan Parsons 

A. E. G. Rummelsburg . . . . 

Erste Brunner 

Chic-Edison Curtis 

A. E. G. Moabit 

Carville Parsons 

Bergman 

Zoelly Charlottenburg 

Erste Brunner 

Zoelly Augsburg Nurnberg 

Boston Edison Curtis 

Richmond Allis 

Brown Boveri 

City Elec. Westinghouse . , 

B. R. T. Westinghouse. . . . 

Manchester Howden 

N. Y. E. Westinghouse 

N. Y. E. Curtis No. 10.... 
Varberg DeLaval 



6,257 
2,177 
6,000 
8,191 
3,169 
5,164 
1,545 
2,052 
2,000 
1,250 
5,195 
4,328 
3,500 
8,563 
11,601 
6,383 
9,870 
8,921 
1,570 



204.0 
198.5 
191.0 
199.0 
185.0 
215.0 
195.0 
200.0 
161.5 
188.0 
189.0 
186.0 
162.0 
183.0 
192.0 
203.0 
192.0 
190.0 
172.3 



176.0 
272.0 
194.0 
143.0 
215.0 
121.0 
201.0 
202.0 
118.0 
204.0 
142.0 
108.0 
133.0 

59.0 
114.0 
137.0 

97.0 
111.0 
170.5 



29.02 
29.32 
28.12 
29.36 
29.00 
28.96 
28.54 
28.39 
27.82 
28.79 
28.74 
27.97 
28.80 
28.10 
27.82 
27.40 
27.19 
28.10 
28.49 



11.95 
11.77 
12.58 
12.68 
12.70 
13.18 
12.97 
13.05 
13.84 
13.10 
13.52 
14.02 
13.72 
14.43 
14.23 
14.30 
15.05 
14.86 
16.47 



249.4 
257.1 
259.5 
263.9 
268.4 
268.8 
270.3 
271.6 
274.5 
274.5 
276.1 
278.3 
278.6 
280.5 
282.8 
285.8 
294.6 
296.0 
337.9 



190.8 
180.9 
205.6 
184.1 
192.8 
192.4 
199.1 
200.5 
218.4 
196.2 
199.3 
211.6 
203.3 
211.8 
212.3 
213.7 
219.5 
208.8 
206.6 



76.4 
70.4 
79.2 
69.8 
71.8 
71.6 
73.6 
73.9 
79.6 
71.5 
72.2 
76.0 
72.9 
75.5 
75.1 
74.8 
74.5 
70.5 
61.2 



References for 
Turbine 

Dunstan Parsons 
A. E. G. Rummelsberg 
Erste Brunner 
Chicago Edison Curtis 

A. E. G. Moabit 
Carville Parsons 
Bergman 

Zoelly Charlottenburg 

Erste Brunner 

Zoelly Augsburg Nurnberg 

Boston Edison Curtis 

Richmond Allis 

Brown Boveri 

City Electric Westinghouse 

B. R. T. Westinghouse 
Manchester Howden 
N. Y. E. Westinghouse 
N. Y. E. Curtis 
Varberg DeLaval 



Economy Tests of Turbines 
Reference 
London Engineering, Mar. 10, 1911. 
Stodola, p. 404, 4th edition. 
Zeit. V. D. I., Dec. 10, 1910, p. 2104. 
Report on Tests by Breckenridge, 1907. 
Zeit. V. D. I., 1907, p. 386. 
Stodola, 439, 4th edition. 
Zeit. V. D. I., Dec. 10, 1910, p. 2104. 
Escher Wyss Leaflet. 
Zeit. V. D. I., Dec. 10, 1910, p. 2104. 
Zeit. V. D. I., Dec. 10, 1910, p. 2104. 
N. E. L. A. Proceedings, 1907, p. 433. 
Sibley Journal, January, 1911. 
Zeit. V. D. I., Dec. 10, 1910, p. 2104. 
A.S.M.E., Journal, December, 1910, p. 2089. 
Operating Co. 

London Engineer, 1909, p. 462. 
N. Y. E. Tests, 1907. 
N. Y. E. Tests, Whitham, 1907. 
Power, May 3, 1910, p. 798. 



60 



ENGINEERING OF POWER PLANTS 



F. W. Dean (Power, May 6, 1913) gives the following comparative 
figures for steam consumption for reciprocating steam engines and 
steam turbines. 

Guaranteed Steam Consumption 

Pounds per Kilowatt-hour 

(150 lb. steam pressure) 



Capacities, kw 


Engine sat, steam 


100°F. superheat 


Turbine 100°F. super- 




(Vac. = 26 in.) 


heat (vac. - 28 in.) 


500 
1,000 
1,500 
2,000 


18.67 
18.80 
18.80 
18.93 


16.8 
16.9 
16.9 
17.0 


17.7 
18.0 
16.8 
16.6 



Economy of Combined Engine and Turbine. — ^An improvement of 
from 20 to 25 per cent, in steam economy is obtained in combining the 




Fig. 34.— Section of Dake-American turbine. 



THE STEAM ENGINE 



61 



low-pressure turbine with a compound condensing engine of normal 
cylinder proportions, and from 40 to 45 per cent, with the same engine 
non-condensing. 

Considering a single-cylinder Corliss engine in connection with 
the low-pressure turbine, the customer's coal bill could be decreased from 
50 to 60 per cent. 

With the use of a low-pressure turbine the excellent performance 
of large, efficient reciprocating engines can be bettered by about 2.5 lb. 
or over 14 per cent. 

Messrs. Stott and Pigott reported^ the following results from com- 
bining a 7,500-kw. Manhattan-type engine with a 7,500-kw. low-pressure 
turbine. 

(a) An increase of 100 per cent, in maximum capacity of plant. 

(6) An increase of 146 per cent, in economic capacity of plant. 

(c) A saving of approximately 85 per cent, of the condensed steam for return to the 
boilers. 

{d) An average improvement in economy of 13 per cent, over the best high-pres- 
sure turbine results. 

(e) An average improvement in economy of 2.5 per cent, (between the limits of 
7,500 and 15,000 kw.) over the results obtained by the engine units alone. 

CO An average thermal efficiency between the limits of 6,500 and 15,500 kw. of 
20.6 per cent. 

Variable -load Steam Consumption. — The steam consumption given 
both for reciprocating engines and turbines are for full rated load. For 
other loads the economy is not as good. The average variation of 
steam consumption per horsepower-hour or per kilowatt-hour with 
change of load, expressed in terms of per cent, of full-load economy, 
may be taken as: 



Per Cent, of Full Load Steam Consumption 



Load 



Vi H 



Engine, per i.hp,-hr 

Turbine (small non condensing), per b.hp.-hr 

Turbine (large condensing) (1851b. and lOO^R superheated 
steam, 28 in. vac), per kw.-hr 



160 
135 

114 



120 
110 

107 



105 
105 

101 



100 
100 

100 



103 
101 

101 



Duty of Pumping Engines.- 
Duty per million B.t.u. = 



water hp. X 1,980,000 X 1,000,000 



B.t.u. in steam used per hour 
Duty is also expressed in terms of ft. -lb. per 1000 lb. of dry steam, 
but the B.t.u. basis is in more general practice owing to the use of super- 
^A.S.M.E. Journal, March, 1910. 



62 



ENGINEERING OF POWER PLANTS 



heated steam. The duties of small, direct-acting pumps may be as low 
as 15,000 ft.-lb. per 1000 lb. of dry steam. 

The duty, efficiency and economy of large reciprocating triple-ex- 
pansion pumping engines are shown by the following table of '^Official 
Trials." 





Location 


Rated 
capac- 
ity 
mil- 
lions 

of 
U. S. 
gal- 
Ions 


Water 
actu- 
ally 
pump- 
ed, mil- 
lions of 
U. S. 
gallons 
24 hr. 


Net 
head 
pump- 
ed a- 
gainst, 
lb. per 
sq. in. 


i 


Ini- 
tial 
gage 
pres- 
sure 


Indi- 
cated 
horse- 
pow- 
er 


Devel- 
oped 
horse- 
power 


Me- 
chan- 
ical 
effi- 
cien- 
cy 


Dry 

steam 

per 

i.hp.- 

hour 


Duty 


Type 


Per 
thou- 
sand 
lb. of 
dry 
steam 


Per 
one 
mil- 
lion 

B.t.u. 
in 

steam 


Holly 
Holly 


Louisville, Ky. 
Frankfort, Pa. 
Albany, N. Y. 
Brockton, Mass. 
Cleveland, 
Boston, Mass. 
St. Louis, Mo. 
St. Louis, Mo. 
Milwaukee, Wis. 


24.0 
20.0 
12.0 
6.0 
2.5 
30.0 
20.0 
15.0 
12.0 


24.111 
21.219 
12.193 
6.316 
2.142 
30.314 
20.070 
15.121 
12.430 


90.0 
95.7 
139.5 
130.6 
180.7 
61.0 
104.0 
127.0 
121.0 


24.0 
20.1 
22.3 
40.1 
62.3 
17.7 
16.5 
16.4 
20.4 


155.1 
180.2 
153.0 
150.0 
149.6 
185.5 
140.6 
126.2 
124.6 


925.7 


158.7 
801.5 
859.2 
801.6 
673.0 


879.4 
817.0 
726.0 
334.0 
151.9 
747.8 
839.6 
726.3 
618.0 


95.0 


9.641 


195.01 
184.4 
182.1 
170.0 
164.6 
178.5 
181.3 
179.4 
175.4 


164.5 


Holly 








Holly 








Holly 

Allis 

AUis 

Allis 

Allis 


95.8 
93.3 
97.7 
90.6 
91.8 


11.51 
10.33 
10.66 
10.67 
10.82 


148.8 
163.9 
158.8 
158.1 
151.0 



' 109°r. superheat at throttle. 



Complete details of three such pumping engines are presented. 



Make and type 



Holly vertical 



Holly vertical 



Worthington 
horizontal 



Contract price 

Weight, tons 

Capacity, gal., 24 hr... 

Diameter, cyls., in 

Stroke, ft 

Diameter, plungers, in. 
R.p.m 



Condensers 

Steam pressure, lb. gage 

Water pressure, lb 

Duty, ft.-lb. per million B.t.u 

Duty per 1,000 lb. 150° superheated steam 
Duty per 1,000 lb. saturated steam. ..... 

Lhp 



Water hp 

Mech. efficiency 

Steam per w.hp.-hr., lb . 
Steam per i.hp.-hr., lb. 



$124,700 

970 

25,000,000 

32, 60, 90 

5 

36 

21.89 

Jet 
150 
80 

151,000,000 
179,000,000 



$112,679 
970 

25,000,000 
34, 64, 98 

34% 
21.356 

Surface 
160 
108 

160,000,000 
193,500,000 



966 

896 

94.5 

11.071^ 

10.250^ 



1,118 
1,074 
96.3 
10.231 
9.861 



$5,500 

15,000,000 
36, 72 
4 

36M 
13.142 
Jet 
100 
80 



125,000,000 

560 

15.8 



150°F. superheat. 



THE STEAM ENGINE 
Cost of Simple, High-speed Engines. — ■ 



63 



I.hp. 


Cost f.o.b. 


Cost per i.hp. f.o.b. 


Cost erected 


Cost per i.hp. 
erected 


50 


$760 


$15.20 


$910 


$18.20 


75 


910 


12.10 


1,070 


14.30 


100 


1,090 


10.90 


1,270 


12.70 


125 


1,260 


10.00 


1,420 


11.30 


150 


1,410 


9.40 


1,625 


10.80 


200 


1,735 


8.70 


1,990 


10.00 


250 


2,050 


8.20 


2,350 


9.40 




Fig. 35. — Section of 125-kw. two-stage Curtis turbine. 

The above figures are averages of several quotations for different 
makes of engines and serve as a basis for approximate cost estimates. 

The f.o.b. cost in dollars for these engines may be represented by the 
formula 

435 + 6.5 X i.hp. 



64 



ENGINEERING OF POWER PLANTS 



Many such formulae are presented by different writers. Naturally 
they vary considerably in accordance with the types of engines con- 
sidered and the state of the market. 

The average of six such formulae for simple, high-speed engines up to 
500 i.hp. is, cost in dollars = 200 + 10 X i.hp. 

Above 500 i.hp. the approximate formula seems to approach more 
nearly to, cost in dollars = 200 + 6 X i.hp. 

The erecting cost of such engines is reported by Potter^ as 



Engine, 
i.hp. 

75 

100 

150 
300 
450 
600 



Erecting 
cost 

$125 to 150 

150 to 200 

200 to 300 

300 to 400 

400 to 450 

400 to 600 



The erecting costs indicated for the engines listed on page 62 follow 
roughly the formula, erecting cost in dollars = 100 + 0.8 X i.hp., which 
averages about 16.5 per cent, of f.o.b. cost of engine. 

Another set of figures for average costs of such engines, erected, 
including foundations, compiled from the wide experience of one con- 
sulting engineer, is as follows: 



Engine horse- 
power 

Cost per horse- 
power 



10 
$36.50 



12 
$36.00 



14 

$35 . 50 



15 
$35.00 



20 
$34.50 



30 
$28.50 



40 
$21.50 



50 
$17.40 



75 
$15.50 



Cost of Simple Non-condensing Corliss Engines. — The cost of simple, 
low-speed engines may be obtained from the table below. 

It should, however, be borne in mind that the prices given may now 
be seriously affected by steam-turbine competition. When such is the 
case, it is probable that the cost of steam engines may be reduced to 
approximately 70 per cent, of the f.o.b. prices given. 

In order to establish the ratio of cylinder size to horsepower of the 
engine, the dimensions of the various engines are included. 

The horsepowers are based on 80 lb, gage pressure and cut-off at 
J^ stroke. 



^ Power, Dec. 30, 1913. 



THE STEAM ENGINE 



65 




oun %]^n 



66 



ENGINEERING OF POWER PLANTS 

Cost of Simple Non-condensing Corliss Engines 



Size 


Hp. 


Engine 
f.o.b. 


Per hp. 


Founda- 
tion 


Erecting 


Piping 


Total 


Total 
per hp. 


14 X36 


100 


$1,700 


$17.00 


$275 


$175 


$165 


$2,315 


$23.15 


14 X42 


110 


1,800 


16.40 


300 


200 


175 


2,475 


22.50 


16 X 36 


125 


1,950 


15.60 


325 


210 


180 


2,665 


21.30 


16 X 42 


140 


2,000 


14.30 


350 


225 


190 


2,765 


19.75 


18 X 36 


•155 


2,150 


13.90 


375 


240 


200 


2,965 


19.15 


18 X42 


175 


2,350 


13.40 


400 


250 


210 


3,210 


18.35 


18 X48 


200 


2,600 


13.00 


425 


260 


220 


3,505 


17.50 


20 X42 


210 


2,600; 


12.40 


500 


270 


230 


3,600 


17.10 


20 X48 


230 


2,850 


12.35 


525 


275 


250 


3,900 


16.95 


22 X42 


250 


3,000 


12.00 


550 


300 


310 


4,160 


16.65 


22 X48 


280 


3,500 


12.50 


600 


325 


340 


4,765 


17.00 


42 X48 


320 


4,000 


12.50 


700 


375 


390 


5,465 


17.10 


26 X48 


380 


4,650 


12.20 


800 


440 


560 


6,450 


16.95 


28 X 48 


425 


5,150 


12.10 


900 


500 


800 


7,350 


17.30 


28 X54 


450 


5,300 


10.80 


1,050 


575 


950 


7,875 


17.50 


30 X 48 


500 


5,800 


11.60 


1,200 


600 


1,070 


8,670 


17.30 



The variation in prices listed 
application of a positive formula. 

The following will, however, approximate 
closely for preliminary estimates. 



is considerable and precludes the 
the values sufficiently 



Cost in dollars, f.o.b. = 700 + 10 X i.hp. 

The averages of other formulae given by different writers for the cost 
of simple Corliss engines are: 
Up to 400 i.hp. 

820 + 10.3 X i.hp. 
Above 400 i.hp. 

375 + 10.2 X i.hp. 

which are in reasonable agreement with the formula above. 

The erecting cost of these engines, including foundations, seems to 
be from 35 per cent, to 50 per cent, of the f.o.b. cost of the engines, 
averaging about 37 per cent. The following formulae may serve in this 
connection. 
Erecting cost in dollars = 

(up to 400 i.hp.) 275 + 3.5 X i.hp. 
(above 400 i.hp.) 250 + 5.0 X i.hp. 



THE STEAM ENGINE 67 

Cost of Compound High-speed Non-condensing Engines 



Size 


Hp.i 


Cost f.o.b. 


Cost per hp. f.o.b. 


8 and 13 X 12 


60 


$1,190 


$19.85 


8 and 16 X 12 


80 


1,420 


17.75 


10 and 18 X 12 


100 


1,520 


15.20 


11 and 19 X 14 


125 


1,830 


14.65 


12 and 20 X 16 


150 


2,285 


15.20 


13 and 22 X 16 


200 


2,620 


13.10 


15 and 25 X 16 


250 


2,890 


11.55 


16 and 28 X 18 


300 


3,580 


11.90 


17 and 30 X 18 


350 


4,150 


11.85 


20 and 36 X 18 


400 


4,590 


11.50 



1 Hp. based on 100 lb., steam pressure. 

Although these quotations vary considerably, they correspond 
approximately to : 

Cost in dollars = 500 + 10.5 X i.hp. 
The averages of several other formulae for the cost of such engines 
are: 

Cost in dollars = 

(below 250 i.hp.) 775 + 10.5 X i.hp. 
(above 250 i.hp.) 625 + 9.5 X i.hp. 

With no data at hand relating to the cost of setting compound high- 
speed engines, it may be assumed that this item amounts to about the 
same percentage of the initial engine costs as in the high-speed simple 
engine. This will give a basis for forming approximate estimates. 

Cost of Compound Condensing Corliss Engines. — 



Size 


Hp. 


Wt. lb. inc., 


wt. 


Costi 


Cost per 


Foundation 


Total 


Total 


condenser 


^l 


f.o.b. 


hp. 


and erecting 


cost 


per hp. 






Based 


an 100 lb. steam pressure 






14 X 28 X 42 


200 


60,000 


300 


$4,565 


$22.80 


$1,050 


$5,615 


$28.10 


18 X 34 X 42 


300 


85,000 


283 


5,700 


19.00 


1,025 


6,725 


22.40 


20 X 38 X 48 


400 


110,000 


275 


7,300 


18.25 


1,250 


8,550 


21.35 


22 X 42 X 48 


500 


140,000 


280 


8,480 


16.95 


1,400 


9,880 


19.75 


24 X 46 X 48 


600 


170,000 


284 


10,000 


16.65 


1,675 


11,675 


19.45 






Based < 


an 120 lb, steam pressure 






13 X 26 X 42 


200 


60,000 


300 


4,465 


22.30 


1,050 


5,515 


27.55 


16 X 32 X 42 


300 


85,000 


283 


5,500 


18.33 


1,025 


6,525 


21.75 


18 X 36 X 48 


400 


110,000 


275 


7,100 


17.75 


1,250 


8,350 


20.85 


20 X 40 X 48 


500 


140,000 


280 


8,280 


16.55 


1,400 


9,680 


19.35 


22 X 44 X 48 


600 


170,000 


284 


9,900 


16.50 


1,675 


11,575 


19.30 



^ Prices include condensers. 



68 



ENGINEERING OF POWER PLANTS 



The prices given apply to both tandem and cross-compound engines, 
the cost of the former being less than 10 per cent, lower in smaller sizes 
and somewhat greater in large sizes. 

The corresponding approximate forriiulse are: 

Cost in dollars, f.o.b. = 1,800 + 13.6 X i.hp. 
and cost in dollars, f.o.b. = 1,600 + 13.6 X i.hp. 

The average of other formulae for compound Corliss engines up 
to 600 hp. is: 

Cost in dollars, f.o.b. = 1,500 + 9.8 X i.hp. 




Fig. 37. — ^Longitudinal section of Westinghouse turbo-generator unit. 



Another series of average costs for engines, condensers, air and 
circulating pumps is as follows: 



I.hp. 


Cost, f.o.b. 


Cost per i.hp. 


400 


$ 9,500 


$23.75 


500 


11,500 


23.00 


600 


13,500 


22.50 


800 


18,000 


22.50 


1,000 


22,000 


22.00 


1,500 


32,000 


21.33 


2,000 


42,000 


21.00 


4,000 


80,000 


20.00 



THE STEAM ENGINE 



69 



These figures correspond approximately to 

Cost in dollars, f.o.b. = 1,000 + 21 X i.hp. below the 1,000 i.hp. 
size 
and 

Cost in dollars, f.o.b. = 2,700 + 19.3 X i.hp. for 1,000 i.hp. and 
above. 

The cost of foundations and setting seems to be about 18 per cent, 
of the f.o.b. cost of the engine, for units of the sizes given. 

One firm manufacturing Corliss engines of from 200 to 3,000 hp. 
gives the weights of engines as from 200 to 250 lb. per horsepower and 
the price from 6 to 8 cts. per pound. 

Cost of Compound Condensing Engines. — Figures reported by one 
consulting engineer indicate that in general the average cost per horse- 
power, erected, for various types of compound condensing engines is 
approximately as follows: 



Engine, horse- 
power 

Cost per 
horsepower. 



100 

$25 



200 300 

$24 $23 



400 

$22 



500 
$21.50 



600 
$21.25 



700 
$21 



800 
$20.75 



900 
$20.50 



1,000 
$20.25 



1,500 
$19.50 



2,000 
$19 



Cost of steam Turbines. — Small turbines for driving pumps, blowers, 
etc., cost from $20 to $40 per horsepower. 

All types of turbines cost approximately the same. Turbine costs 
are subject to considerable variation, the tendency being a decided 
decrease in the cost per kilowatt from year to year. The costs given 
should therefore be checked against actual quotations, even when used 
in preliminary estimates. 

Approximate Cost of Steam Turbines and Generators 
In Dollars per Kilowatt, Rated Capacity 



Size, kw. 



100 300 500 750 1,000 



2,500 



5,000 



7,500 10,000 



Direct-current condens- 
ing 

60-cycle A.C. condens- 
ing 

25-cycle A.C. condens- 
ing 



48 



38 



36 

22 



30 



28 
16 
25 



13.50 
17.00 



12.00 
14.00 



11.00 
12.50 



10.50 



Approximate formulas for the cost of steam turbines and generators 



are: 



70 ENGINEERING OF POWER PLANTS 

Cost in dollars, f.o.b. = 

(a) (To 40 kw.) 300 + 37 kw. 

(6) (40 to 350 kw.) 30 X kw. 

(c) (1,000 to 10,000 kw.) 8,000 + 11.5 X kw. 

Other formulas distinguish between impulse and reaction types as 
follows : 

Impulse type (turbine alone) 

Cost in dollars, f.o.b. = (To 50 hp.) 170 + H X hp. 

(50 to 400 hp.) 11 X hp. 
Reaction type (turbine generator) 

Cost in dollars, f.o.b. = (500 - 5,000 kw.) 3,000 + 13.5 kw. 

(5,000 - 10,000) 17,500 + 10.5 kw. 

F. W. Dean^ gives the comparative cost of turbine and reciprocating 
engine units on the basis of real outputs at 80 per cent, power factor 
including apparatus and exciters, all erected, including foundations as: 







Comparative Costs 






Capacities, 


Horizontal four-valve engine units 


Turbine units 




kw. 


Total cost 


Cost per kv.a. 


Total cost 


Cost per kv.a. 


turbine 


500 


$22,700 


$45.40 


$12,250 


$24.50 


1.85 


1,000 


40,200 


40.20 


17,900 


17.90 


2.24 


1,500 


62,200 


41.50 


23,800 


15.85 


2.61 


2,000 


76,400 


38.20 


30,500 


15.25 


2.50 



FIELDS OF ENGINES AND TURBINES 

Commercial Aspects of the Turbine. — ^Limitations. The field of the 
turbine is limited by its relatively high speed and the fact that it is non- 
reversible. Because of its high speed it should not be used for driving 
machinery by belting. In view of this restriction the turbine is limited 
to driving direct-connected apparatus, such as electric generators, 
centrifugal pumps, fans and blowers, ship propellers, etc. The use of 
reduction gearing has enlarged the field of the turbine and increased its 
usefulness. .The turbine is essentially a central station apparatus. 

Field of the Reciprocating Engine. — The power for rolling mills, blast 
furnaces, mine and water- works pumping, mine hoisting, air and am- 
monia compressors, etc., will be furnished by the piston engine for a 
long time, and Corliss engines or similar types will still be used for mill 
work where belt or rope driving is preferred. 

^ Paper before National Association of Cotton Mfgrs., Boston, April, 1913. 



THE STEAM ENGINE 71 

Turbine Advantages. — The advantages of the turbine are high 
economy under variable loads, small floor space, uniform angular velocity 
and close speed regulation, freedom from vibration, inexpensive founda- 
tions, ease in erecting and usually quickness in starting, steam economy 
not seriously impaired by age, small cost of maintenance and attendance, 
adapted to use with high superheat, water of condensation free from 
oil. 

Engine Advantages. — Rather than call attention to special features 
engine builders point to reliability, simple and cheap condensing system 
requiring only a small quantity of condensing water, and to the fact 
that nearly as good economy as the best turbine economy may be ob- 
tained without the use of highly superheated steam. 

It is only fair to say that in the last 5 years all of the builders of 
large-sized engines for land work have practically gone out of business, 
although many engine builders still remain in the field. It is noticeable 
that only the builders of the higher-class engines and the lower-class 
engines in the medium and small sizes remain in the field. 

Turbines vs. Engines in Units of Small Capacity. — Under this title 
K. S. Barstow presented the following summary before the A.S.M.E. 
in December, 1915, for units of less than 500-hp. capacity. 

APPLICABILITY OF TURBINES 

1. Direct-connected units, operating condensing 60-cycle generators in 
all sizes, also 25-cycle generators above 1,000-kw. capacity. (This paper is, 
however, not intended to deal with units of this size.) 

Direct-current generators in sizes up to 1,000-kw. capacity, including ex- 
citer units of all sizes. 

Centrifugal pumping machinery operating under substantially constant 
head and quantity conditions, and at moderately high head, say from 100 ft. 
up, depending upon the size of the unit. 

Fans and blowers for delivering air at pressures from l^-in. water column 
to 30 lb. per square inch. 

2. Direct-connected units, operating non-condensing for all the above 
purposes, in those cases wherein steam economy is not the prime factor or 
where the exhaust steam can be completely utilized, and, in the latter case, 
particularly where oil-free exhaust steam is desirable or essential. 

3. Geared units, operating either condensing or non-condensing for all 
the above-mentioned applications, and in addition, many others which would 
otherwise fall in the category of the steam engine, on account of the relatively 
slow speed of the apparatus to be driven. 

APPLICABILITY OF ENGINES 

1. Non-condensing units, direct-connected or belted and used for driving: 
Electric generators of all classes excepting exciter sets of small capacity, un- 



72 



ENGINEERING OF POWER PLANTS 




less belted from the main engine. 
Centrifugal pumping machinery, 
operating under variable head and 
quality conditions and at relatively 
low heads, say up to 100 ft., de- 
pending on the capacity of the 
unit. Pumps and compressors for 
delivering water or gases in rela- 
tively small quantities and at 
relatively high pressures in the case 
of pumps at pressures above 100 
lb. per square inch and in the case 
of compressors at pressures from 
1 lb. per square inch and above. 

Fans and blowers (including 
induced draft fans) for handling air 
in variable quantities and at rela- 
tively low pressures, say not over 
5-in. water column. 

Line shafts of mills, where the 
driven apparatus is closely grouped 
and the load factor is good. 

All apparatus requiring reversal 
in direction of rotation, as in hoist- 
ing engines and engines for traction 
purposes. 

2. Condensing units direct- 
connected or belted, for all the 
above purposes, particularly where 
the condensing water supply is 
limited, and where the water must 
be recooled and recirculated. 

The Saving of Space.— The 

introduction of the composite 
type of machine has made 
possible large improvements in 
the space requirements of tur- 
bines. At the present time 
60,000 kw. in turbines with 
their condensing apparatus can 
be placed in the space occupied 
by 8,000 kw. of vertical engines 
with direct-connected genera- 
tors and jet-condensing appa- 
ratus. A few years ago, three 



THE STEAM ENGINE 



73 



20,000-kw. machines were placed in the space formerly occupied by 
four 4,500-kw. engine units. A few years earlier an 8,000-kw. turbine 
was placed in the space occupied by a 4,000-kw. vertical engine. 
Where horizontal engines have been in use the space saving is of course 
much larger and 60,000 kw. could be placed today with its condensing 
apparatus in the space occupied by a 1,500-kw. duplex tandem com- 
pound horizontal unit. In the smaller sizes the saving of space is nearly 
as well marked, but is always a function of the speed of the turbine, slow- 
speed turbines being very large and high-speed turbines comparatively 
very small. A 250-hp. medium-speed non-condensing turbine can be 
put inside of a 4-ft. cube, and a 150-hp. high-speed turbine might be 
put in a 30-in. cube. There seems to have been no great saving in 
space with the vertical-shaft turbine over the horizontal-shaft turbine 
when condensers and auxiliaries are taken into account. 

Based on the overall dimensions of the generating units but not includ- 
ing condensers and auxiliaries, W. F. Fisher reports {Power, vol. 34, pages 
275) the average approximate floor space per engine horsepower to be : 
Comparative Space per E.hp. 





Turbine units 


Corliss engines units 


Capacities, hp. 


Type 


Sq. ft. 
per e.hp. 


Type 


Sq. ft. 
per e.hp. 


2,000 
2,000 
5,000-8,000 
5,000-8,000 
5,000-8,000 


Westinghouse-Parsons 
Curtis horizontal 
' Westinghouse-Parsons 
Curtis horizontal 
Curtis vertical 


0.146 
0.098 
0.100 
0.060 
0.040 


Horiz. cross-comp. 

Vert, cross-comp. 

Manhattan 

Vert, three-cyl. comp. 


0.64 
0.36 
0.48 
0.20 



A ratio of the average space occupied by the engine units to that of 
the turbine units reported is 4.7 to 1. 

A similar table has been compiled from a paper by F. W. Dean^ 
based on real output of the units at an 80 per cent, power factor. Besides 
the generating units, the condensing apparatus and exciters are included. 
Comparative Space per Kixovolt-ampere 





Turbines 


Engines 




kw. 


Dimensions, 
ft. 


Sq. ft. per 
kv.a. 


Dimensions, 
ft. 


Sq. ft. per 
kv.a. 


turbines 


500 
1,000 
1,500 
2,000 


14 X 6 
14 X 8 
19 X 9 
21 X 9 


0.168 
0.112 
0.114 
0.094 


18 X 26 
24 X 30 
26 X35 
28 X37 


0.935 
0.720 
0.605 
0.518 


5.57 
6.43 
5.30 
5.51 



Paper before National Association of Cotton Mfgrs., Boston, April, 1913. 



74 



ENGINEERING OF POWER PLANTS 



Although the possibiUties of great space reduction by instalhng 
turbines in place of reciprocating engines are clearly shown by the 
figures given above, it is peculiarly interesting to note that the present- 
day tendency toward less-crowded conditions in central stations makes 
the actual space reduction per kilowatt of plant rating less real than 
generally supposed as shown by the following tables compiled from 
published^ data from 23 well-known central stations. 

1. Capacity, ult. kw. 

2. Boiler capacity, ult. hp. 

3. Boiler hp. per rated kw. 

4. Square feet per kw. (ground-floor plan). 

5. Square feet per kw. (total single-deck plan). 

6. Square feet per kw. (total generating room). 

7. Square feet per kw. (net gen. room exc. switchboard). 

8. Square feet per kw. (boiler room actual floor plan). 

9. Square feet per kw. (boiler room total single-deck plan). 
10. Square feet per boiler hp., boiler room (single-deck plan). 











5 Corliss, 


vertical and 


horizontal 






18 Turbines 






engines 




T, ,- ^ 
















Ratio ^ 




A, Max. 


B, Min. 


C, Avg. 


D, Max. 


E, Min. 


F, Avg. 


1 


77,500 


3,000 


30,000 


70,000 


38,500 


50,000 




2 


62,500 


2,500 


22,500 


43,000 


23,000 


33,500 




3 


0.948 


0.435 


0.71 


0.833 


0.614 


0.67 


0.945 


4 


3.46 


0.817 


1.84 


1.985 


0.958 


1.44 


0.783 


5 


3.46 


1.206 


2.04 


3.01 


1.33 


2.24 


1.10 


6 


1.71 


0.30 


0.81 


1.16 


0.634 


0.82 


1.01 


7 


1.15 


0.208 


0.59 


0.784 


0.524 


0.65 


1.10 


8 


1.746 


0.49 


1.13 


1.063 


0.384 


0.66 


0.585 


9 


1.746 


0.679 


1.28 


2.12 


0.768 


1.42 


1.110 


10 


2.65 


0.778 


1.77 


2.75 


1.08 


2.10 


1.19 



In modern well equipped plants using moderate sized boiler units, 
the average boiler room space will be 2 to 2.5 sq. ft. per boiler horsepower. 

Similarly for a fairly compact turbo-generating room, the space will 
average from 0.75 to 1.15 sq. ft, per horsepower. 

If 0.67 boiler horsepower be allowed per kw. and 2.25 sq. ft. of floor 
space be allotted per boiler horsepower, the floor space per kw. will 
average 1.5 sq. ft. 

First Cost vs. Economy of Operation. — The first cost of engines of 
the different types in a measure varies inversely as the economy and 
durability, but as a rule the saving in the coal bill due to the operation 

1 " Recent Developments on Steam Power Station Works," by J. R. Bibbins, paper 
before A. S. and T. Ry. E. A., 1907 convention. 



THE STEAM ENGINE 



75 



of. engines of the better grade will more than pay the excess in the first 
cost during the first few years of operation, which in some respects might 
be considered as paying interest on the investment. 

It is not always true that plants containing the most expensive 
engines have as a whole the highest initial cost, as the more economical 




Fig. 38, — Comparative size of 1000-hp. pumping engine and 2500-hp. torpedo-boat 

engine. 



type of engine requires less boiler capacity, and the saving in boiler- 
room cost may be enough to cover the extra engine cost. 

For convenience it may be stated that a boiler horsepower requires 
the evaporation of approximately 30 lb. of water at the usual tem- 
peratures of feed water and at ordinary steam pressures. 

As already seen the amount of steam required by different engines 
varies from about 10 lb. per horsepower-hour in best practice to 50 or 
60 in poor grades of engines. 



75a ENGINEERING OF POWER PLANTS 

This would indicate that with the most economical types of engines 
1 boiler horsepower would be sufficient to supply 3 engine horsepower, 
while with the poorer types 1 boiler horsepower would supply steam 
for about }i an engine horsepower. In one case the boiler would have 
to be of six times the capacity of the other to supply the same amount 
of power. • 

This may be put in another form as follows: 1 boiler horsepower = 
33,480 B.t.u. per hour. 

In reasonably large plants an indicated horsepower = 12,000 to 
24,000 B.t.u. per hour. 

Then in general in large plants it is sufficient to provide only enough 
boiler horsepower to equal one-half the engine indicated horse poweras 
this will not only meet the normal engine demand for steam, but will 
give sufficient margin to cover the cutting out of boilers for cleaning 
and repairs. 

For small amounts of power or for intermittent use inexpensive 
engines will prove satisfactory, but when the cost of power is a large 
item and when the engine is run continuously, the best is none too good. 

Engines are usually designed to give the rated power when working 
with the best ratio of expansion. The most economical use of steam is 
usually found, therefore, when engines are working under normal fuU 
load, provided they are working under favorable conditions. Engines 
must be properly proportioned for the load they are to carry, if high 
economy is to be maintained. The best results are invariably found with 
engines operating under steady load. In electric-power stations the 
load generally varies within wide limits and a number of tests of such 
stations shows that the same grade of engine consumes about 50 per 
cent, more steam for the same work than for service where the load is 
uniform. 

Compounding is advisable for large units if the load is reasonably 
uniform. With a fluctuating load the simple engine governs better and 
is about as economical. 



PROBLEMS 

1. General Problem. — Power Plant Analysis. — 

This analysis involves an inspection of and report upon an existing power plant; 
preferably a small, or medium sized isolated plant rather than a large central station. 
The report should cover: 

I. An analysis of the initial investment; 

II. An analysis of the cost of power production; 

III. A study of the general arrangement with a view to criticism and possible 
improvement. 

The following suggestions may serve as a guide for the analysis. 



THE STEAM ENGINE 756 

Investment for : " 

1. Location. 

With an analysis of the location showing general characteristics, nearness 
to railroads, probable cost of excavation, character of ground as affecting 
foundations, etc. 

2. Buildings. 

Type, form of construction, materials used, cubic contents, floor area, cost per 
cubic foot, cost per square foot, cost per horsepower or per kilowatt, etc. 
(a) Boiler room. 
{b) Engine room, 
(c) General storage buildings if any. 

3. Coal storage facilities outside of boiler room. 

4. Trackage, etc. 

5. Stacks. 

Type; cost of various bases; general data as regards height, diameter, area 
and its relation to other portions of the equipment. 

6. Boiler room equipment: 

(o) Boilers; type, important dimensions of drums, tubes and setting, draft, 

flue areas, etc. 
(6) Coal storage and coal handling equipment, giving a general outline of this 

installation. 
(c) Ash handling equipment, giving a general outline of this portion of the 

equipment. 
id) Auxiliary devices such as feed pumps, feed water heaters, economizers, 

feed water regulators, damper regulators, induced or forced draft 

equipment, and all special equipment, 
(e) Piping with sizes for each piece of apparatus as well as the main lines, 

type of valves, fittings, provision for expansion, drainage, etc. Be 

sure to give this portion of the installation careful attention, discussing 

its arrangement from all standpoints. 
(/) Water supply and purification. Special equipment necessary. Discuss 
effect on the operation of the boilers, etc. 

7. Engine room equipment. 

(a) Engines; type, manufacturer, rating, stroke and diameter of piston, 

speed, pipe sizes, any special equipment such as oilers, etc. 
(6) Foundations, dimensions and information regarding subsoil, etc., as 

related to the cost of foundations. Was piling required? Did the 

foundations require special forms for molding? 
(c) Generators with all related data, such as rating, voltage, amperes, direct 

current or alternating, belted or direct-connected, etc. 
{d) Condensers; type, cooling surface, air pumps, and circulating pumps with 

all related data. 
(e) Piping with all data for boiler room piping. 
(J) Switchboard, with instruments, etc. 
{g) Special equipment such as fire-pumps, air compressors, traveling cranes, 

etc. 

General Instructions. — - 

1. In all of this work sketches showing the location of apparatus should be made 
giving general dimensions and pipe sizes. 

2. Obtain information regarding grade of fuel used and the location from which 



75c ENGINEERING OF POWER PLANTS 

it comes; the exact mine if this is known. The total amount of coal used will serve 
for checking your calculations. 

3. If a load curve for the plant is available it will prove of great assistance. , Lack- 
ing such information, watch the switchboard instruments for a time, obtaining read- 
ings. Such data will help in making up a probable load curve. 

4. Determine the number of engineers and firemen employed and their hours of 
labor. 

5. Where heating is done obtain an idea of the heating surface supplied with 
exhaust and live steam. Such information may be approxmate but it will assist in 
establishing the probable figures. 

6. Secure data on the amounts used and cost of oil, waste and supplies. 

7. If cost data is freely given, accept it by all means, but such points should not 
be pressed. 

8. After having a complete list of the entire installation, make a. table listing the 
apparatus, etc., with actual costs or assumed costs. All cost figures should be re- 
duced to cost per horsepower or per kilowatt where possible. 

9. Take precaution to obtain complete data even though some items may seem 
insignificant at the time. 

10. _ Analyze the data and estimate the cost of power production. 

11. Study the general arrangement making criticisms with a view to possible 
improvement in equipment and layout. 

Form for Presentation of Report: — 

(a) All work must be neatly written in ink or typewritten on white, unruled 
paper of the standard size required in the mechanical engineering department. 

(6) On the front page insert the title, date, etc., as illustrated: 

Power Plant 

OF THE 

. John Smith Manufacturing Company, 

236 Main Street, Philadelphia 

Power Plant Analysis 

By a. B. Clark 

University of 192. . 

(c) Calculations should be neatly arranged and must be on separate sheets bound 
with the other data. 

(d) The report covering item I is due , 192. . . The report 

covering items II and III is due , 192. . . 

2. Engine is 12 in. by 18 in. Piston rod 2 in.; m.e.p. for head end = 40 lb. and for 
crank end = 37 lb.; 250 r.p.m. Find (a) Horsepower of head end. (h) Horsepower of 
crank end. (c) Total indicated horsepower (i.hp.). 

3. Engine is 6 in. by 9 in. Piston rod 1)4= in.; m.e.p. for head end = 33 lb. and 
crank end = 30.5 lb.; 300 r.p.m. Find same as in problem 1. 

4. A locomotive running at the rate of 45 miles per hour has 72-in. driving wheels 
and cylinders 18 in. by 30 in. Piston rod 2}4 in.; m.e.p. 100 lb. Find the indicated 
horsepower of the locomotive. 

6. In problems, 2, 3 and 4, find the horsepower constant for both head and crank 
end of each engine. 



THE STEAM ENGINE 7hd 

6. An engine is required to indicate 37 hp. with m.e.p. = 40 lb., stroke = 18 in., 
r.p.m. = 90. Required the diameter of the cylinder. 

7. Test the "Handy Rule" on page 19 in problems 2, 3 and 6. 

8. A small factory has a 450-i.hp. simple, high-speed, non-condensing engine and a 
450-i.hp. compound, low-speed, condensing engine. If the steam used by the two 
engines is allowed to waste, what will be the actual difference and per cent, difference 
in the steam consumption of the two engines for a month of 26 days, when operating 
at full load for 10 hr. each day? 

9. What size compound, high-speed, non-condensing engine would give the same 
total steam consumption as the 450 i.hp. simple engine in problem 8? 

What size compound, high-speed, condensing engine would give the same total 
steam consumption? 

10. In a recent engine test the following readings were secured : (a) When running 
non-condensing; length of run, 10 hr.; reading of feed-water meter at beginning of test, 
26,958.7 cu. ft. and at end, 27,324.5 cu. ft.; average temperature of feed water at 
meter, 195°F.; voltmeter, 230; ammeter, 130. (6) When running condensing; time, 
10 hr.; feed-water meter, 34,652.0 and 34,911.6; feed water, 120°F.; load as in {a). 
Find the water consumption per e.hp.-hr. and the per cent, gain by running con- 
densing. 

11. Check the thermal efficiency and B.t.u. per i.hp.-hr. for plants Nos. 2, 13 
and 36 pp. 55 and 56. 

12. Check B.t.u. per kw.-min., Rankine cycle B.t.u. per kw.-min. and efficiency 
ratio for the following plants listed in the lower half of p. 59. 

{a) Dunstan Parsons. 
(6) Boston Edison Curtis, 
(c) N. Y. E. Westinghouse. 

13. A mine hoisting drum on the main shaft of a simple, high-speed, non-con- 
densing engine is located directly over the shaft. A load of 3,000 lb. is lifted vertically 
at the average rate of 175 ft. in 10 sec. While in operation the steam consumption 
of the engine is at the rate of 3,240 lb. per hour. 

What is the steam consumption per indicated horsepower per hour? 

14. A mine hoisting drum on the main shaft of a simple, high-speed, non-con- 
densing engine is located directly over the mine shaft. 

During a test of the unit the following data were secured. Weight lifted vertically, 
1 ton (2,000 lb.). 

Rate of lift, ft. per sec. Steam consumption per hour, lb. 

, 10 2,020 

17.5 2,860 

25 3,500 

35 4,32C 

50 6,370 

Determine : 

(a) Steam consumption per i.hp. hour for each rate of lift. 

(6) Normal i.hp. rating of the engine. 

(c) Steam consumption per b.hp. hour for each rate of lift. 



76 ENGINEERING OF POWER PLANTS 

15. Given the following data for a steam pumping engine: 

Diameter cylinders, inches 32 60 90 

Diameter piston rods, inches 3 6 9 

(rods pass entirely through cylinders) 

Stroke, feet 5 

M.e.p., pounds 68 19 8.5 

Water pumped per 24 hr., gallons 36,000,000 

Head on pumps, or lift, feet 160 

Steam used per hour (containing 2 per cent, moisture) 

pounds 12,500 

Guaranteed duty, foot-pounds, per 1,000 lb. dry 

saturated steam 140,000,000 

Bonus, $1,000 per million ft.-lb. above 140 

Forfeiture, $2,000 per million ft.-lb. below 140 

R.p.m 21.8 

Determine : 

1. The indicated horsepower of the engine. 

2. The water horsepower of the engine and the mechanical efficiency. 

3. The consumption of dry saturated steam per hour per indicated horsepower and 
per water horsepower. 

4. The bonus or forfeiture, if any. 

16. The following is the operating performance of a two and three quarter (2^i) 
million gallon centrifugal pumping unit consisting of two pumps (in series), gear- 
driven by a condensing steam turbine. 

Discharge head = 158 lb. per square inch. 

Suction lift = 12 ft. 

Rate of pumping = 1,890 g.p.m. 

Steam per hour = 3,965 lb. 

Steam pressure = 150 lb. per square inch gage and dry saturated. 

Exhaust pressure = 0.5 lb. per square inch absolute. 

Determine : 

1. The water horsepower; 

2. Pounds of steam per water horsepower-hour. 

3. Duty per million B.t.u. 

How does this duty compare with the average performance of reciprocating triple- 
expansion pumping engine? What considerations might justify the installation of the 
lower duty centrifugal unit? 

What brake horsepower rating should be specified for the turbine in the above case? 

17. For purposes of preliminary estimate, determine the approximate size of 
building (square feet of floor area) for a steam-turbine installation of 3,000-kw. 
capacity. 

(a) Turbine room; 
(6) Boiler room; 
(c) Plant. 

18. Determine the heat economy, thermal efficiency, and efficiency ratio of the 
169-hp. Buckeye-mobile described on pages 53. and 56. 



CHAPTER ITI 

EFFICIENCY AND COST OF ELECTRIC GENERATORS AND 

MOTORS 



Efficiency and Cost. — The discussion of electric transmission of power 
and of the relative merits of the D.C. and A.C. systems will be presented 
later. The efficiency and cost of this type of equipment are, however, 
presented at this point. 

Efficiency of Generators. Per Cent. 



Kw. 


Load = Vi 


H 


H 


^4 




50 


72.0 


81.0 


84.0 


88.0 




100 


74.5 


83.5 


86.0 


91.0 




250 


76.0 


85.5 


89.0 


93.0 




500 


77.5 


87.0 


90.5 


94.5 




750 


78.0 


87.5 


91.0 


95.0 




1,000 


78.0 


88.0 


91.5 


95.5 




1,500 


78.5 


88.5 


92.0 


96.0 




2,000 


79.0 


89.0 


92.5 


96.5 




5,000 


79.0 


89.0 


92.5 


96.5 





The efficiency of generators at other than full load may be found 
approximately from the following table. 

Efficiency of Generators in Per Cent, of Full-load Efficiency 

Per cent, of rated load ^^^ *'^efficfency""^°^'^ 

100 100.0 

90 99 . 4 

80 98.4 

70 96.8 

60 94.7 

50 92.0 

40 88.0 

30 84.0 

With direct-connected engine-generator sets in which the sizes of 
the two machines are properly proportioned to each other, the individual 
efficiencies may be combined, giving the following combined mechanical 
and electrical or the overall full-load efficiencies and relative efficiencies 
with fractional loads as indicated on p. 78. 

A convenient 'method for the conversion of kilowatt generator rating 
to indicated horsepower engine rating is by combining into one factor the 

ratio ' ^ (746 watts = one hp.), or 1.34, and the above overall efficiencies. 

For example, the 50-kw. generator set will require at 75.3 per cent. 

77 



78 



ENGINEERING OF POWER PLANTS 



Full load 


Fractional load 


Rating of generator, 


Per cent, overall efficiency 


Per cent, of the rated load 


Per cent, of the full-load 


kw. 


of unit 


on generator 


overall efficiency of unit 


50 


75.3 


100 


100.0 


100 


78.5 


90 


98.5 


250 


82.8 


80 


96.1 


500 


85.4 


70 


92.6 


1,000 


87.7 


60 


89.0 


1,500 


89.5 


50 


84.5 


2,000 


91.2 


40 


79.4 


3,000 


91.5 


30 


72.5 






20 


62.9 






10 


50.8 



50 X 1.34 
overall efficiency, an engine indicated horsepower rating of — ^ „' — = 

50 X 1.78 = 89 i.hp., 1.78 being the resultant conversion factor. These 
factors will be as follows for the several sizes listed. 

Conversion Factor (Full Rated Load) 

Rating of generator, Factor 

50'. 1 .78 

100..... 1.71 

250 1 . 62 

500 1.57 

1,000 1 . 53 

1,500 1.50 

2,000 , 1 . 47 

3,000 1 .465 

At fractional loads the factors must be increased with the deaease 
of the overall efficiency. The conversion factor corresponding to the 
unit rating may be divided by the proper per cent, of full-load overall 
efficiency or may be multiplied by its reciprocal. The reciprocals of 
the per cent, values in the above table, expressed as multipliers, are 
given below. 

Fractional Load Multiplying Factor 

Per cent, load on generator Factor 

100..... 1.00 

90 1.015 

80 1.04 

70 1.08 

60 1.12 

50....; 1.18 

40 : 1.26 

30 1.38 

20 1.53 

10 1.97 



ELECTRIC GENERATORS AND MOTORS 



78a 



The approximate cost of generators and motors is contained in the 
following tables and diagrams: 

Direct-current Belted Generators,'^ Cost per Kilowatt 



Kw. 


Slow-speed 


Moderate-speed 


High-speed 


5 




$37.00 (1,200 r.p.m.) 

28.50 (1,000 r.p.m.) 

16.00 (1,300 r.p.m.) 

8.50 (1,000 r.p.m.) 


$30.00 (1,800 r.p.m.) 


10 




23.00 (1,800 r.p.m. ) 


25 
100 


$17. ©0 (900 r.p.m.) 
12.30 (675 r.p.m.) 



Other cost data for D.C. belted generators may be obtained from the 
following formulas: 

Capacity Cost in dollars, f.o.b. 

To 10 kw. (1,200-2,200 r.p.m.) 20+30 X kw. 

10 to 300 kw. (600-1,400 r.p.m.) 200 + 9 X kw. 

For estimating the cost of direct-current direct-connected generators, 
the following formulas may be useful. 

Capacity Cost in dollars, f.o.b. 

To 300 kw. (100-350 r.p.m.) 300 + 11 X kw. 

300-1,000 kw. (moderate speed) 600 + 10 X kw. 

Alternating-current Belted Generators 



Kv.a. 


Speed 


Cost per kT.a. 


15 


1,800 


$22.50 


25 


1,800 


18.00 


100 


900 


14.00 


500 


360 


10.00 



Check values may be obtained from the formula: 

Capacity Cost in dollars, f.o.b. 

To 300 kv.a. (600-1,800 r.p.m.) 150 + 11 X kv.a. 



Alternating-current Direct-connected Generators 



Kv.a. 



50 

75 

250 

500 

1,000 



Speed 



300 
277 
200 
120 
100 



Cost per kv. 



$20.00 
17.00 
11.00 
11.00 
10.00 



^ These costs of generators per kilowatt are taken from the section on costs, " Ma- 
chine Shop Electrical Handbook," by C. E. Clewell, McGraw-Hill Book Co., N. Y. 



786 ENGINEERING OF POWER PLANTS 

A check formula is • 

Capacity Cost in dollars, f.o.b. 

To 300 kv.a. (200-300 r.p.m.) 500 + 9 X kv.a. 

300-2,500 kv.a. (100-250 r.p.m.) 2,500 + 6 X kv.a. 

For the cost of motors, a combination of several quoted prices and 
formulas results as follows: 

Type Capacity Cost in dollars, f.o.b. 

D.C. belted To 2 hp. (1,400-2,500 r.p.m.) 20 + 40 X hp. 

2-30 hp. (1,000-1,800 r.p.m.) 50 + 12.5 X hp. 

30-100 hp. (500-800 r.p.m.) 200 + 11 X hp. 

30-100 hp. (800-1,000 r.p.m.) 225 + 8 X hp. 

D.C. variable To 10 hp 65+35 X hp. 

speed Above 10 hp .* 70 + 10.5 X hp. 

A.C. single-phase 

(110-2,200) To 25 hp. (1,200-1,800 r.p.m.) 30 + 11 X hp. 

A.C. polyphase 

induction To 125 hp. (1,200-1,800 r.p.m.) 125+ 4.5 Xhp. 

A.C. variable To 25 hp 50 + 8 X hp. 

speed 30-60 hp 150 + 4 X hp. 




$100 $200 $300 $400 $500 $600 $700 $800 $900 

Fig. 39. — Cost of direct-current shunt and compound motors. 115 and 230 volts. 



ELECTRIC GENERATORS AND MOTORS 



79 



50 



40 



{§20 



10 



























v6 




f/ 








f 


K/ 


( 


/ 








/ 


'// 













/ 


^ 


/y 


/^ 








i 


^ 


^ 













$400 



$500 $600 $700 $800 



$100 $200 $300 

Fig. 40. — Cost of direct-current shunt and compound motors. 550 volts. 
(Prepared by L. B. Beatty, 1915.) 




Motors above 7.5 H.P. Supplied 
>'■"' with Starting Compensators 

-Note: Motors 5 H.P. and Under not Supplied 
with Starting Compensators 



$100 



$200 



$300 



$400 



$500 $600 $700 

!FiG. 41. — Cost of induction motors — squirrel-cage. 110 to 550 volts, 60-cycle. 

(Prepared by L. B. Beatty, 19] 4.) 



80 



ENGINEERING OF POWER PLANTS 




$100 .^0 $300 $400 $500 

Fig. 42. — Cost of induction motors — phase-wound. 

2'cj> and 3-</». 

(Prepared by L. B. Beatty, 1915.) 



$700 $800 

110 to 550 volts, 60-cycle, 



50 



^40 
o 



30 



XI 20 
O 



























/ 


/ 
























// 


/ 






















i 


/ 


/ 




















f' 


'f\ 


% 


f 




















f 


'4^ 


w 


\j 
























^A 


/ 


' 




















/ 




V 






















/ 


r/ 


/ 






















J 


/J 

























J 


/ 





/ 
























\y 


/ 



















100 



500 



600 



100 



ZOO 200 ^0 

Cost in Dollars 
Fig. 43. — Cost of induction motors — phase wound. 110 to 550 volts, 60-cycle, 

2-0 and 3-^. 
(Prepared by L. B. Beatty, 1915.) 



Switchboard prices vary considerably. For switchboards including 
dynamo and feeder panels, average prices for 220 volts or less may be 
taken from the following table, bearing in mind that these average figures 
are subject to a possible variation of 30 per cent, above or below the 
averages given. 



ELECTRIC GENERATORS AND MOTORS 



81 



D.C. 


A.C. 


Kw. 


Average $ per kw. 


Kv.a. 


Average $ per kv.a. 


25- 50 

50-100 

Above 100 


7.50 
6.00 
4.50 


50-150 

150-400 

Above 400 


5.00 
3.50 
2.50 



PROBLEMS 

19. The engine of problem 10 is a simple, high-speed unit. 

(a) What was the approximate steam consumption per brake horsepower-hour un- 
der the two conditions of the test shown? 

(6) What was the approximate steam consumption per indicated horsepower-hour 
under the two conditions? 

20. A test of a compound Corliss engine with D.C. generator, direct-connected, 
gave the following readings when running non-condensing : 

Length of run, 5 hr. 

Water-meter readings, 72,850 and 73,500 cu. ft. 

Voltmeter, 240; ammeter, 1,500. 

What was the approximate steam consumption per indicated horsepower-hour? 

21. The owner of a small factory has installed two simple high-speed non-condens- 
ing steam engines with direct-connected D.C. generators. 

Engine A is guaranteed not to consume more than 63 lb. of dry saturated steam per 
kilowatt-hour at full load. At the time of the test the following data were obtained. 

Cylinder diameter = 10 in. 

Stroke = 15 in. 

Diameter piston rod = 2 in. 

M.e.p. head end = 40 lb. 

M.e.p. crank end = 42 lb. 

R.p.m. = 250 

Total steam used per hour = 2,100 lb. 

Engine B is guaranteed not to consume more than 29 lb. of dry saturated steam per 
indicated horsepower-hour at full load. At the time of the test the following data 
were obtained. 

Voltmeter reading = 230 

Ammeter reading = 230 

Total steam used per hour = 2,850 lb. 

1. Was engine A safely within the guarantee? 

2. Was engine B safely within the guarantee? 

3. Which engine showed the better economy? Approximately how much better? 

22. The following are the full-load performances of a 500-kw. direct-connected 
engine and a 500-kw. turbo-generator operating under conditions as noted: 



Steam consumption, lb. per hr. 



Initial pressure, lb. per sq. in, 
gage 



Vacuum, in. of Superheat 
Hg. °F. 



Engine . 
Turbine. 



13,750 
10,700 



125 
150 



25.5 

28.5 

(30-in. 

barometer) 



(dry) 
100 



82 



ENGINEERING OF POWER PLANTS 



Determine for each and compare: 

(a) The steam economy in pounds per kilowatt-hour. 

(6) The heat economy in B.t.u. per kilowatt-hour. 

(c) The thermal efficiency in per cent. 

(d) The heat economy of a Rankine cycle for the conditions given, in B.t.u 
kilowatt-hour. 

(e) The efficiency of a Rankine cycle for the conditions given, in per cent. 
(/) The efficiency ratio. 

23. A guarantee for steam consumption for a 750-kw. unit with simple, con 
densing low speed engine and D.C. generator, using saturated steam is as follows: 



per 



Per cent, load on generator 

125 
100 

75 

60 

40 

20 



Lb. steam per kw.-hr. 

35.0 
25.0 
27.5 
33.0 
47.0 
70.0 



Verify these guarantees showing details and state whether or not the guarantees are • 
good. 

24. Three manufacturers of electrical hoisting equipment have each entered one 
D.C. unit in competitive tests. The selection of the unit is to be made on the basis 
of minimum steam consumption when developing 200 i.hp. as this is the average load 
demand. 

The tests records were as follows: 





Unit A 






Unit B 






Unit C 




Volts 


Amperes 


Steam per 
hr., lb. 


Volts 


Amperes 


Steam per 
hr., lb. 


Volts 


Amperes 


Steam per 
hr., lb. 


240 


1,000 


11,050 


238 


960 


11,800 


241 


830 


10,700 


239 


810 


8,600 


240 


830 


9,450 


238 


755 


9,100 


241 


700 


7,600 


239 


700 


7,700 


240 


690 


8,150 


240 


500 


6,100 


241 


540 


6,350 


239 


480 


6,000 


238 


300 


4,650 


242 


320 


4,650 


241 


280 


4,200 



(a) What was the normal i.hp. rating of each engine? 

(6) Which engine shows the best economy on the basis called for in the specifica- 
tions? 



CHAPTER IV 
FOUNDATIONS 

1. Must support concentrated weight of engine upon the ground by distributing 
the weight over sufficient area to prevent setthng. 

2. Must go far enough below surface to be beyond setthng either from frost, vibra- 
tions, or influence of loads borne by adjacent ground. Rarely safe to permit a depth 
less than 3 ft. below the general level. In cold regions effect of frost is felt down to a 
depth of 6 ft. The foundations for small engines are rarely less than 43^ ft., while for 
large units the depth is sometimes as great as 20 to 25 ft. Engine foundation depths 
are usually decided by other considerations than weight, such as location of auxiliaries, 
cellar or basement, etc. 

3. Must have mass and weight enough to hold engine still against unbalanced 
forces. 

4. Must have mass enough to take up vibrations if bedplate is not massive enough. 

The rules for allowable weight per square foot on different soils vary 
in different cities, but in general the supporting power in tons per square 
foot may be taken as (Baker, ''Treatise on Masonry Construction"): 

Rock — granite, etc., in hard compact strata 200 to 

Rock — ^limestone, equal to best masonry 25 to 30 

Rock — sandstone, equal to best brick masonry 15 to 20 

Rock — ^broken and well compacted 7 to 20 

Rock — soft and pliable as shale, equal to poor brick masonry 15 to 20 

Hard pan — gravel and sand, well cemented with clay 8 to 10 

Clay — ^thick beds and dry 4 to 6 

Clay — ^thick beds and moderately dry 2 to 4 

Clay — ^sof t, wet, confined 1 to 2 

Gravel — coarse and dry, well compacted and confined 8 to 10 

Sand — dry, compact, well cemented with clay 4 to 6 

Sand — clear and dry, confined in natural beds 2 to 4 

Quicksand — marshy and alluvial soils, etc., confined . 5 to 1 

If the soil is of low bearing power, piling must be used. Formerly 
piles were usually of spruce or hemlock. At the present time yellow 
or red pine, oak, birch and beech are used. Steel piles and concrete piles 
are also meeting with favor. 

Wooden piles are at least 5 in. in diameter at the point and 10 in. 
at the butt for piles 20 ft. or less in length; 6 in. at the point and 12 in. 
at the butt for piles over 20 ft. long. 

The "Engineering News Pile Formula," often used, is, safe bearing 
power in tons = twice the weight of hammer in tons multiplied by 
height of fall in feet divided by one + penetration of pile in inches 
under last blow. 

83 * 



84 ENGINEERING OF POWER PLANTS 

Often the tops are cut level and the soil excavated for a foot. Con- 
crete is then filled in over the heads of the piles, sometimes to a depth of 
several feet. 

The Metropolitan Street Ry. 96th Street power house, New York 
City, and the Kent Avenue Power House, Brooklyn, are on 8-ft. beds of 
concrete over piles 30-in. centers. 

Engine Foundations Proper. — The engine builder always furnishes an 
engine foundation plan, showing the various footings which must be 
supported and the location and sizes of the various anchor bolts. It is 
customary to build a wooden template covering the entire foundation 
and supporting square wooden boxes about 1)4 in. larger internally 
than the diameter of the foundation bolts. These act as forms and 
when removed from the foundation allow plenty of play for the founda- 
tion bolts. The heavy cast-iron washers or anchor plates are set in the 
concrete form at the base of these boxes and pockets are provided below 
them so that the nut on the lower end of the foundation bolt may be 
reached by a wrench. At the present time foundations are always built 
of concrete in monolithic masses as far as possible, and the foundation 
is usually allowed to set a week or 10 days before any heavy weights are 
placed upon it. 

Good concrete is made by mixing 1 part of good Portland cement, 
3 parts of sand and 5 parts of broken stone or gravel, the latter small 
enough to pass through a 2-in. ring. This should be mixed very wet. 

Another proportion sometimes used for engine foundations is 1 : 2 : 4. 

Concrete foundations weigh approximately 150 lb. per cubic foot. 

Cost of Concrete Foundations. — ^Large foundations or foundations 
of the simplest form may be put in for from $6 to $8 per cubic yard. 

If the foundations are small or irregular, requiring special forms 
and considerable template work the price will often be about double the 
above figures or $13 or $14 per cubic yard complete, including all ex- 
cavating and carpenter work. 

Another basis of estimating foundation costs is: 

Excavation without shoring in soft material 50 cts. to $1 per cu. yd. 

Excavation without shoring in rock $1 to $4 per cu. yd. 

Concrete $6 to $7 per cu. yd. 

Forms. 15 cts. per sq. ft. 

Waterproofing (if used) 40 cts. per sq. ft. 

Average cost figures for concrete work of a large project recently reported^ 
are: 

Group 1.— For plain concrete used for walls, approaches, bins, con- 
duits, etc. 

Group 2. — Miscellaneous concrete foundations. 

^See "Unit Construction Costs" by E. H. Jones, McGraw-Hill Book Co. 



FOUNDATIONS 



85 



Group 3. — Reinforced-concrete walls, foundations, sumps, etc. 
Group 4. — Items 1, 2 and 3 combined. 



Group 

No. 


■ 

Total amount, 
cu. yd. 


Labor cost per cu. yd. 


Material cost per 
cu. yd. 


Total cost per cu. yd. 


Max. 


Min. 


Avg. 


Max. 


Min. 


Avg. 


Max. 


Min. 


Avg. 


1 

2 
3 

4 


7,779 

8,706 

2,830 

19,315 


$8.07 
6.85 
7.49 
8.07 


$0.75 
2.01 
3.40 
0.75 


$2.85 
2.99 
3.37 
3.37 


$8.82 
8.90 
9.48 
9.48 


$3.37 
3.42 
6.42 
3.37 


$4.82 
5.36 
5.48 
5.48 


$16.11 

13.52 
16.35 
16.35 


$5.53 
6.00 

10.35 
5.53 


$7.67 
8.36 

13.53 
8.85 



Anchor Bolts 




'•■Pockets 



Fig. 44. — Foundation for cross-compound engine. 

The cost of foundations for engines, condensers and pumps will 
average not far from 



Engine hp. 

200 

400 

600 

800 
1,000 
1,500 
2,000 



Cost 
1,000 
1,600 
2,100 
2,700 
3,300 
4,700 
6,100 



A consulting engineer of large experience shows the cost of all the 
foundations required in steam-power plants to be approximately as 
follows : 



86 



ENGINEERING OF POWER PLANTS 

Cost of Foundations per Engine Horsepower 



For Simple Non-condensing: 

I.hp. of plant 

Cost per horsepower 

For Simple Condensing: 

I.hp. of plant. 

Cost per horsepower 

I.hp. of plant 

Cost per horsepower 

For Compound Condensing: 

I. hp. of plant 

Cost per horsepower. 

I.hp. of plant 

Cost per horsepower 



.10 
$5.70 



10 
$8.50 



40 
$7.00 



100 
$5.70 



700 
$5.10 



12 
$5.50 



12 

$8.40 



50 
$6.70 



200 
$5.60 



800 
$5.00 



14 
$5.40 



14 
$8.30 



75 
$6.00 



300 
$5.50 



900 
$4.90 



15 
$5.35 



15 
$8.10 



100 
$5.70 



400 
$5.40 



1,000 
$4.80 



20 
$5.25 



20 
$7.80 



500 
$5.30 



1,500 
$4.40 



30 
$5.15 



30 

$7.40 



600 
$5.20 



2,000 
$4.10 



40 
$5.05 



50 
$4.90 



75 
$4.60 



Foundation Bolts. — Foundation bolts for small engines are rarely 
below % in. in diameter and from this they increase in size with the 
engine and the stresses to 23^ to 3 in. on large vertical engines up to 
10,000 hp. These bolts may be of medium steel and the larger sizes 
always have upset ends with the threads of a larger size than the body 
of the bolt. They should not be too long on account of temperature and 
stress changes, but should run down far enough into the foundations 
to get sufficient weight of concrete between the engine bed and the 
anchor plate. The anchor plates are always of cast iron, designed 
after the manner of column bases and usually have lugs cast on their 
bottom surface to hold the lower nut. 

It is not customary to use locknuts on anchor bolts, but they are 
sometimes used, especially for vertical engines on those bolts which pass 
through the bearings and are also used to hold down the bearing caps. 

Grouting. — The bedplate, after being placed on the foundation, 
is lined up and leveled by means of shims and steel wedges. After this 
is done the anchor bolts are inserted and the nuts tightened up hand- 
tight, using a proper wrench for the size of the nut. This leaves a 
joint between the bedplate and the foundation, which varies from J"^ in. 
in small engines to 1 to l}^ in. in large engines. A clay dam is now 
built around the bedplate and cement grout, usually neat or at worst 1 
part cement to 2 parts sand, is poured into this space through holes which 
are left for this purpose in the bedplate. Where the bedplate is hollow 
it is quite customary to fill it with this cement grout. Care must be 
taken that there are no air bubbles left under the bedplate and that the 
cement runs out until held by the dam on all sides of the bedplate. The 
grout is now allowed to set for 3 or 4 days, the dam and the ragged 
edges of the grout chipped away and then the foundation bolt nuts 



FOUNDATIONS ' 86a 

are tightened to full bearing by sledging, taking care that the alignment 
and the level of the bedplate are not changed. 

Other materials have been used instead of the cement grout, such as 
a rust joint made out of iron filings and sal ammoniac, melted sulphur, 
type metal, oakum, felting and in some cases even wooden wedges, but 
at present practically the only material used is the cement grout. 

Alignment. — If the bedplate is in one casting, as is usual in small 
engines, it is only necessary to level up the planed surfaces of the guides 
in two directions at right angles to each other, and even this is not 
absolutely necessary. Where the bedplate is in two or more parts the 
various sections are assembled on the foundations in approximately their 
final positions. They are then bolted together, or the T-headed links 
are heated and placed in the holes provided for them, thus bringing the 
parts of the bedplates into close contact by the shrinking of the links. 
The bedplate, then, as a whole is wedged up until it is level in both 
directions. 

It is frequently necessary during this period, especially in vertical 
engines, to have one part of the bedplate slightly higher than its final 
position in order that the deflection caused by the added weights placed 
on the plate may just bring the bedplate to a true level. This work 
will be greatly expedited by the use of an engineer's level, although on 
smaller engines it is customary to level and center the bedplate from 
wires which have been stretched through the final axis of the cylinder 
and shaft. With large shafts and with considerable distance between 
the bearings there will be measurable deflection, in which case, with ver- 
tical engines, the cylinders will not be set in the vertical plane, but will 
be inclined so that the cylinder axis will be at right angles to the shaft 
in its deflected position. The cylinders of a 5,000-hp. cross-compound 
vertical engine, with the flywheel and generator between the cylinders 
may be as much as J^g in. closer together than the centers of the cranks. 
In one case on an engine of this size where the generator and flywheel 
were outboard of the engine, the outboard bearing had to be set nearly 
^i in. above a true level to produce quiet and cool running. 



PROBLEMS 

25. Estimate the size and cost of foundations for the following steam engines. 
(a) 50-hp. simple high-speed. 

(6) 500-hp. tandem compound CorUss. 

(c) 2,000-hp. Manhattan-type Corhss compound. 

26. The dimensions of bedplate of a 1,000-kw. turbo-generator are 6 ft. 6 in. by 17 
ft. in. The distance from basement floor to turbine-room floor is 14 ft. The soil 
below basement level is moderately dry clay. Sketch a proposed foundation for the 
turbine and estimate the cost of the same. 



866 ENGINEERING OF POWER PLANTS 

27. Eight steam-engine and generator units of 2,500 kw. each, weighing with 
auxiliaries 350 lb. per indicated horsepower, are to be erected on a pile foundation. 
The area covered is 100 ft. by 100 ft. Piles, 4 ft. center to center. In driving the piles 
a 2,000-lb. hammer was used; drop, 10 ft. ; last penetration of pile, 1 in. Is the founda- 
tion safe? If so, how much leeway is there for each pile, in pounds? If not safe, how 
much excess load is there for each pile, in pounds? 



CHAPTER V 

CONDENSERS 

Condensation may be considered as of two kinds; mixed condensation 
when the steam and cooling water are brought together in the same 
vessel or machine as in the jet, barometric and ejector types, and surface 
condensation when a film of metal prevents mixing as in the surface 
and atmospheric types. 

5TEAM ENTRANCE 
K 





Parallel-flow type 



Counter-current type 



Fig. 45. — Barometric condenser heads. 



Mixed Condensation. — 

Let ts be the temperature of the steam to be condensed. 
to be the temperature of the injection water. 
t\ be the temperature of the outlet or hotwell water. 
H be the total heat in the steam at ts. 
h be the heat in the liquid at h, 
w be the pounds of steam per hour to be condensed. 
Q be the pounds of water per hour needed for condensing. 



Then 



R = 



H 



(1) and R is the ratio of water to steam 



M/ tl to 

required for condensation. 

tl theoretically is equal to t, but in practice ti is from 5° to 10° lower 
than tt owing to the presence of air and imperfect mixing. In pro- 

87 



88 



ENGINEERING OF POWER PLANTS 



portioning ordinary jet or barometric condensers w is the normal amount 
of steam to be condensed and a 50 per cent, overload is common at 
some reduction of vacuum. 

Let G = the cubical contents of the cone in cubic feet. 
Then G = OMUSw + 8.25 cu. ft. (2) 

The allowable velocity in the tail pipe is 5 ft. per second. 
Then J = 0.073 V^ in. (3) 

A = 15.7 VG in. (4) 

B = 0.3A 
C = h2A 

J-1 for small sizes. 
J-2 for large sizes. 

"5 for 26-27 in. Increase slightly for 28 in. 



H 



I = 



{ 



Steam velocity in K about 600 ft. per second. 

fw 

= Vso 



K 



abt. 



(5) 



The height of the flange x above the level of the hotwell should 
never be less than 35 ft. and may be greater to advantage. 



Size of condenser, 
lb. of steam per hr. 


5,000 


10,000 


15,000 


20,000 


25,000 


30,000 40,000 


50,000 


60,000 


80,000 


100.000 


Exhaust K 

Tail pipe J 

Injection H 

Air I. . . . 


10'' 

6 

5 

2 
38 

9 
45 
28 
56 


14" 

8 

7 

3 
45 
13 
54 
33 
66 


17" 

9 

8 

3 
48 
14 
57 
36 
72 


20" 
10 

9 

3 

52 
16 
62 

38 
76 


22" 
11 

10 
4 
56 
17 
- 67 
40 
80 


24" 
12 
11 
5 
60 
18 
72 
42 
84 


28" 
14 
12 
5 
63 
19 
75 
46 
92 


32" 
16 
14 
6 
68 
20 
81 
50 
100 


35" 

18 

16 
6 

72 
, 21 

86 

52 
104 


40" 
20 
18 
7 
78 
23 
94 
57 
114 


45" 
24 

20 

8 


Diameter A 

B 

C 

D 

E 


82 
25 
99 
60 
120 



The condenser bell should be as near to the exhaust flange as possible 
as friction and velocity head count up very fast with good vacua. The 
barometric pipe may be replaced by a pump of some kind. In the 
ordinary jet condenser the bell is placed over the suction chamber of the 
pump. In all arrangements of this type there must always be a suf- 
ficient head of water over the suction valves to ensure their rising. 

Ejector condensers follow the same principle as the ordinary type 
when a tail pipe is used and the throat of the ejector is usually figured 
for a velocity of 15 to 20 ft. per second. 

Here K = \/^ as before, inches 
H = 0.073 Vw ~ lin. 



CONDENSERS 



89 



T - O.QH in. _ 
J = 0.073 \/w in. 
= 5K about 

The flange X should be about 40 ft. above the level of the tail water. 

T 



ilnjectionl 





Fig. 46. — Ejector condenser, 
Bulkley type. 



\^-G—^ 



Fig. 47. — Ejector condenser, 
Schiite & Koerting type. 





SCHUTTE EdUCTOR CoNDENSER 






Pounds steam per hour 


A 


B 


c 


D 


E 


G 


520 


9 


6^ 


3M 


2 


m 


IM 


1,040 


123^ 


8 


43^ 


3 


2 


2 


2,240 


18K 


11 


5 


4 


3 


3 


3,300 


213^ 


13 


5^ 


5 


33^ 


33^2 


4,800 


25M 


15 


63^ 


6 


4 


4 


6,600 


30^ 


17 


7M 


7 


4K 


43^ 


9,000 


353^ 


19 


8 


8 


5 


5 


12,000 


41 


213^ 


9 


9 


6 


6 


15,000 


463^ 


233^ 


10 


10 


7 


7 


21,000 


53 


27 


11 


12 


8 


8 . 


28,500 


61^ 


30 


12 


14 


9 


9 


36,000 


70 


34 


14 


16 


10 


10 


24,000 


80 


38 


15 


18 


12 


12 


60,000 


90 


43 


18 


20 


14 


14 


90,000 


108 


51 


21 


24 


16 


16 



90 ENGINEERING OF POWER PLANTS 

Ejector condensers without the tail pipe are common and when 
properly installed and operated work very well. 

Condenser bells of most any shape may be used and are equally 
efficient if the water and steam are brought into contact and the air is 
collected and carried away. This may be done by a separate dry air 
pump, or the air pipe may be led into the throat of the tail pipe. 

Surface Condensation. — The steam is condensed on the outer surface 
of metallic tubes through which the condensing water flows. 

Let N = total heat to be transmitted per hour, B.t.u. 
S = outside surface of tubes, total in square feet. 
dm — mean temperature difference of water and steam, °F. 
K = coefficient of heat transmission, B.t.u. per square foot 
per hour, per °F., diff. in temperature. 

Then N = KOmS Q = w ^-^ (6) 

ti — to 

and N = w{H - h) S = '^^^ ■ = '^^^^ (7) 

Let ta = vacuum temperature. 

For practical work K may be taken as constant for any one con- 
dition, although it has been shown by experiment to be subject to small 
variations with dm* 

The mean temperature difference for rough calculation with small 
rise in temperature of the circulating water may be the arithmetical 
mean without serious error, but for most calculation the geometrical 
mean should be used. 

e» = -^-^ (8) 

1 1-5 I/O 

The quantity of circulating water Q is a function of the number and 
size of the tubes, the number of water passes in the condenser and the 
velocity of the water in the tubes. The values of K depend on the 
velocity of the water also as well as on the material of the tube, its 
cleanliness and the richness of the steam and air mixture in the condenser. 

The general formula for K is K =' kcp^Uy/y^ (9) 

Where k equals 350 a constant, 

c equals the cleanliness coefficient varying from 1.0 to 0.50, 

Pa 

p equals the air richness ratio ^• 

U equals the material coefficient. 

1.0 for copper. 

0.98 for admiralty mixture. 

0.97 for admiralty mixture oxidized. 



CONDENSERS 91 

0.95 for Muntz metal. 
0.92 for aluminum bronze. 

Vyj — water velocity in tubes, feet per second. 
The water velocity should be about 8 ft. per second although 5 ft. is more 
usual. The material coefficient may usually be taken at 0.95 and the 
cleanliness coefficient at about 0.9 for such waters as New York or 
Chicago. The air richness coefficient is exceedingly difficult to measure 
experimentally but for tight condensers with efficient air pumps it may 
be taken at from 0.95 to 0.97. Under these conditions K = 782. The 
value oi K = 782 is thus under the best conditions and should not be 
taken for design since tight condensers and air pumps are not the rule 
but the exception and tubes soon oxidize or become coated with dirt and 
scale. In commercial work K = 350 seems to be the usual figure but 
values as high as 600 have been guaranteed. It should be remembered 
that a surface condenser is rarely tested to its limit. 

In condenser design the given quantities usually are Wj to and the 
required vacuum. It is important that the place of measurement of 
the vacuum should be stated and this is usually in the nozzle connect- 
ing the prime mover to the condenser. The best vacuum will always 
be found at the air-pump suction, less in the body of the condenser, and 
the worst in the nozzle. The vacuum inside the prime mover will be 
less by the velocity head necessary to give motion to the exhaust and by 
friction in the nozzle. The allowable velocity in a turbine nozzle is 
about 600 ft. per second. 

Starting with the vacuum in the nozzle certain assumptions must 
be made; first, the loss in the condenser known as drop — this in a well- 
designed condenser should not exceed 0.2 in. of mercury and tg should 
be taken as the temperature corresponding to this reduced vacuum. 
For good practice ti should be from 8° to 10°F. lower than ta and h — to 
is now known. H and h are known from the steam tables and Q may 

be calculated. — the ratio of cooHng water to condensed steam usually 

ranges from 50 to 100 and it should be remembered that a large ratio 
means more power required in the circulating pumps. 

Having ts, to and ^i the mean temperature difference may be calculated 
from (8) and the surface from (7). 

Small tubes are best for the transmission of heat but cannot be used 
with dirty water so that the usual sizes are % in., % in., 1 in. and in some 
cases with very bad water IJ^ in. or even larger. 

Let a = area of tube in square inches. 

I = length of tube in feet (sum of all passes). 
d = diameter of tube in inches. 



92 ENGINEERING OF POWER PLANTS 

n = number of tubes in one pass. 
A — area of one pass in square feet. 
/ = number of passes. 

Then 

_ 144A _ Q 
'^ ~ a ~ l,560a7,. ^^"^ 

and 

'-5? <n) 

The length of a single tube is -^ and the tube ratio is -^. This should 

be between 30 and 50. The best value of this ratio has not been estab- 
lished by experiment. 

Some adjustments may be necessary due to space and other con- 
siderations which can be made at this time. 

Tube spacing is important as there must be room for the glands 
and sufficient metal between them for strength. The minimum allow- 
able spacing or pitch of tubes is 

%-in. tubes l^e-in. pitch 192 tubes per square foot. 

^-in. tubes IKe-iii- pitch 147 tubes per square foot. 

%-in. tubes lyi -in. pitch 106 tubes per square foot. 

1 -in. tubes 1% -in. pitch 88 tubes per square foot. 

13^-in. tubes 1% -in. pitch 63 tubes per square foot. 

The number of tubes per square foot of tube-sheet surface is given 
roughly by n = ^^^,. 

Glands should be of the same metal as the tubes and be provided 
with an inside lip to prevent creeping of tubes. The entrance of the 
gland should be rounded. 

Rubber rings are much used for packings on European condensers 
with fresh condensing water, but the screw gland with corset-lace pack- 
ing put in with an automatic gun is probably best. Tube packings 
may be fiber, woven hose or corset lacing. No animal or vegetable fats 
should be used on the packing as they form soluble compounds with 
copper, paraffine is the best wax to use with woven packings. 

Tube sheets should be Muntz metal or brass. A rolled sheet will 
give the best service although cast sheets are used. The thickness of 
tube sheets should be J^ in. to % in. larger than the tube diameter. 

Condenser shells are usually of cast iron ribbed outside against 
collapsing pressure but may be of steel plate or sheet brass (navy practice) 
stiffened with angles. Tubes should be supported at distances of 60 to 



CONDENSERS 



93 



70 diameters by supporting plates usually of cast iron, drilled with Ji^e-i^- 
clearance around the tube. 

Water boxes should be large and designed to offer as little friction 
as possible to the passage of the water. A hole 3-^ in. in diameter in the 
partition will allow the upper box to drain when not in use and the 
condenser is usually set on a slope of 1 in. in 15 ft. so that the tubes 
may drain. Where possible the steam should enter from the top and 
water at the bottom (counter-current principle) but this is not essential 
as parallel flow condensers give good results. 



tXHAUST STEAM INUt 




Fig. 48. — Cross-section spiroflo surface condenser. 



The bottom of the circulating water outlet should be above the 
highest point of the tube bank. If this cannot be done at the water 
box the pipe should be carried up to the same height away from the 
condenser. 

The steam passage should be direct to the tube bank and if possible 
the nozzle should be spread so no dead spots may be left away from the 
path of the steam. The upper bank of tubes may have a wider spacing 
than the lower or channels may be left open into the tube surface to afford 
a free passage for the steam. Baffle-plates and guide plates are also 
used for the same purpose but are not as efficient. 

The steam flow should be directed to the coldest part of the condenser 
and here the dry air suction should be taken out. The suction should 
be screened to prevent water being carried into it. 



94 



ENGINEERING OF POWER PLANTS 



Water connections should be figured for a velocity of 10 ft. per 
second and the air connection should be at least twice the hotweli water 
size which should be figured for about 3 ft. to 4 ft. per second. 

Owing to the wide range of steam consumptions for engines no 
definite relation exists between engine horsepower and required con- 
denser surface. Similarly no definite relation exists between the con- 
densing surface and the amount of steam condensed unless the cooling 
water temperature is constant. An average figure commonly quoted 
is 10 lb. of steam condensed per hr. per square foot of condensing surface 
for 24 to 26-in. vacuum with 70°F. cooling water. 




Fig. 49. — Cross-section Westinghouse surface condenser. 



Although the circulating water required per pound of steam con- 
densed varies widely in practice, depending on the vacuum maintained, 
the difference between the temperature of the steam due to the vacuum 
and the temperature of the condensate leaving the condenser, and the 
amount of air in the condenser, yet the following figures will serve as 
an indication of the variation in the amount of circulating water required 
due to differences in initial temperature of the circulating water. 



CONDENSERS 



Pounds circulating water per pound steam condensed = R = 



95 

H -h 



ti — to 

Practical Results. Condensing water leaving condenser 5° below 
steam temperature ti = ts — 5. 



Vac. 


H-h 


u 


h 


R 


to = 50 


to = 60 


fo = 70 


<o = 80 


24.0 


1012 


141 


136 


11.8 


13.3 


15.3 


18.0 


25.0 


1017 


133 


128 


12.0 


15:0 


17.5 


20.8 


26.0 


1022 


125 


120 


14,6 


17.0 


20.5 


25.6 


27.0 


1028 


114 


109 


17.5 


21.0 


26.4 


35.4 


28.0 


1036 


100 


95 


23.0 


29.6 


41.5 


69.0 


28.5 


1041 


90 


85 


29.8 


41.7 


69.5 


209.0 


29.0 


1049 


77 


72 


47.5 


87.0 


525.0 





Theoretical Results. 
ti = ts. 



Condensing water leaving at steam temperature 



24.0 


1012 


141 


141 


11.1 


12.5 


14.3 


16.6 


. 25.0 


1017 


133 


133 


12.3 


13.9 


16.2 


19.3 


26.0 


1022 


125 


125 


12.6 


15.7 


18.6 


21.7 


27.0 


1028 


114 


114 


16.1 


19.0 


23.4 


30.2 


28.0 


1036 


100 


100 


20.7 


25.9 


34.5 


52.0 


28.5 


1041 


90 


90 


26.0 


34.7 


52.0 


104.0 


29.0 


1049 


77 


77 


38.8 


61.5 


150.0 





Surface condensers should be used v/hen suitable boiler feed water 
is not easily obtained. If, however, suitable water for the boilers is 
easily obtained, the jet condenser should be used. It is simple and 
relatively inexpensive. 

Condensing Apparatus for Turbines. — It has been definitely proved 
that the reciprocating engine is ill adapted to utilize a vacuum higher 
than 26 in. The turbine, on the contrary, can easily utilize vacuums of 

28 in. and with proper design of 29 in. and even 29)^-^ in. The con- 
densing apparatus necessary to furnish a 28-in. vacuum will be nearly 
double the size of that required for 26-in. The ratio of condensing 
water to condensate, instead of being 25 at 26 in. vacuum, varies from 
80 to 110 at vacuums above 29 in., thus largely increasing the size 
of the circulating pumps and water piping. The hotwell pump is small 
in any case, but where reciprocating air pumps are used the size for 

29 in. will be largely in excess of that for 28 in., while with the engine 
condenser no dry air pump is required. If rotary air pumps of the 
Le Blanc type are used, the space occupied will be about half the size 
of the circulating pump. Steam jet air pumps require little room. 

With the larger turbines of the present day and basements 20 to 25 
ft. in the clear, it is possible to arrange all of this condensing apparatus 



96 



ENGINEERING OF POWER PLANTS 



under the space occupied by the turbine unit and the necessary aisles 
around it. This will not be possible if a concrete foundation is used, 
and in most of the modern installations the turbine is supported on a 
structural-steel foundation which at the same time supports the con- 
densers, condenser piping and operating room floor (see Engineering 
News, January 14, 1915, p. 66). 




Fig. 50. 



AIR OUTLET 



WATER OUTLET. 

-Cross-section contraflo surface condenser. 



Air Condensers. — Condensers in which air is used instead of cooling 
water are not common in steam engineering but are used where water 
is scarce and bad. The steam to be condensed is led into pipes or 
chambers of thin plate around which the air is circulated either by a 
chimney or fan. A notable condenser of this type was installed at 
Kalgoorlie, Australia, to condense 32,000 lb. of steam per hour. The 
condenser consisted of corrugated-steel sheets spaced J^ in. apart. The 
steam flowed inside the compartments, the air being circulated by a 
fan. In all about 43,000 sq. ft. of cooling surface was installed. A 
22-in. vacuum was obtained with outside air at 42°F. With outside air 
at 113°F. no vacuum was obtained. The average was about 18 in. for 
the year. The fans took about 10 per cent, of the station output at full 
load. 



CONDENSERS 



97 



Gebhardt gives for the value of heat transmitted from steam to air 
through 3^^-in. steel corrugated plates, 10 to 25 B.t.u. per hour per 
square foot per degree difference of temperature for air velocities of 500 
to 4,000 ft. per minute. 




■ 



^m>^ 



m 



Fig. 51. — Section through Beyer barometric condenser. 



Evaporative Condensers. — In this type of condenser the steam is con- 
densed in plate or tube condensers by evaporating the cooling film 
of water. These condensers are common in refrigerating, brewery and 
similar industries. A slow air circulation is necessary to carry off the 
moisture-laden air. The heat transmission is quite good. With cast- 
iron pipes about 1 sq. ft. of surface is required per pound of steam per 
hour and vacuums up to 25 in. are readily maintained. With brass 



98 ENGINEERING OF POWER PLANTS 

tubes and good circulation about 8 lb. may be condensed per hour per 
square foot of surface. The power for fans and pumps should not 
exceed 5 per cent, of the output (see paper by Oldham, Proceedings 
I.M.E., 1899). 




Fig. 52. — Koerting eductor and multijet condensers. 



Pennel in Kansas City built a number of evaporative condensers 
which are interesting. He secured a 25-in. vacuum with a cooling 
water evaporation equivalent in weight to 43 per cent, of the steam 
condensed (see Power, Jan. 12, 1909, page 128). He used a stack to 
secure the air circulation. Usually in evaporative condensers the weight 
of water evaporated is equal to from 50 to 90 per cent, of the weight of 
steam condensed. In another type built in Chicago a horizontal steel 



CONDENSERS 99 

shell is provided with heads in which are expanded a large number of 
small brass tubes. The outlet end is provided with a cone leading to 
the exhaust fan which pulls the air through the tubes. The steam to be 
condensed is led between the tubes. Water is sprayed into the open 
ends of the tubes with the air. 

Condenser Auxiliaries. — These may be classified as : 
(a) Circulating pumps which supply the cooling water at a sufl&cient 
pressure to overcome friction and velocity heads. 

(6) Hotwell or condensate pumps which serve to remove the conden- 
sate only from the condenser and deliver it against the atmospheric 
pressure. 

(c) The wet air pump of which there are many varieties. 

1. The air pump which not only removes the condensate and non-condensible 
vapors but also removes the cooling water which has been delivered to the con- 
denser by atmospheric or other pressure. 

2. The air pump which only handles the condensate and non-condensible vapors. 

3. The air pump which is a combination condensate pump and wet and dry air 
pump. There are a number of designs of this type. 

(d) The reciprocating dry air pump handling only the non-conden- 
sible vapors. This pump may be simple, compound or duplex. 

(e) The water-jet air pump which is of many types. 

1. The plain ejector type, single- or multiple-jet with separate pump. 

2. The combined pump and ejector. 

3. The pump and disk-jet type. 

4. The pump and multiple-jet type. 

5. The slug type with single or multiple diffuser. 

(/) The steam jet air pump. 

Circulating Pumps. — The circulating pump supplies the cooling water 
to the condenser at a sufficient pressure to overcome the friction and 
velocity heads. 

Plunger pumps, directly driven from the prime mover, were first 
used for this purpose and were quite satisfactory, but large and costly. 
The head is usually small, not over 20 ft. where the highest point in the 
circulating system does not exceed 30 ft. above the water level. The 
lower end of the discharge pipe can always be submerged and this con- 
dition maintained but the excess head must always be pumped against. 

It was found that better results could be obtained by separating pump 
and prime mover and the first independent circulating pumps were 
plunger pumps of the direct type without flywheels. 

To save space and weight the centrifugal circulating pump was 
introduced in marine practice and has now replaced all others for sta- 
tionary practice as well. It may be driven by an engine, motor, or 
steam turbine either directly or through gearing or belting. For small 



100 



ENGINEERING OF POWER PLANTS 



sizes the best, cheapest and most satisfactory unit is the motor or steam- 
turbine driven unit directly coupled, the type of drive depending on the 
type of station. For large work the low-speed pump is driven by a 
high-speed motor through reduction gearing, and for very large work 
the pump may have two or three rotors in one casing. Pump efficiencies 
of 60 per cent, are usual and by careful design 70 per cent, can be 
attained. 

Where a supply of water is available above the condenser level, 
circulating pumps may be dispensed with entirely and there are a few 

installations where the condenser 
may be worked without pumps of 
any kind. Such an installation 
may be seen at Rochester, N. Y., 
where ejector condensers without 
pumps are in use giving 27 in. of 
vacuum. 

Condensate Pumps. — Separate 
condensate pumps are a compara- 
tively late innovation and are either 
of the direct-acting or centrifugal 
type. The direct-acting pumps 
have not been much used since 
the development of the centrifugal 
condensate pump. Centrifugal 
pumps for this service are never 
large, a 6-in. pump being sufficient 
for the largest unit. They were 
formerly built in two stages, but 
since the conditions under which 
they work have become better 
understood single-stage pumps 
have been employed. The head is 
rarely over 60 ft. of which 30 ft. 
may be due to the vacuum in the condenser and the rest friction and delivery 
head in the discharge line. These pumps should always be horizontal 
top discharge to avoid air pockets and the suction connection should 
be so designed as to be always submerged. The runners may be venti- 
lated to the upper part of the hotwell, but if the suction piping is short 
and direct and the suction submerged this is not necessary. 

The condensate and circulating pump may be combined in certain 
forms of mixed condensers with good results. The old jet condensers, 
Fig. 53, were examples of this type and the newer centrifugal jet, Fig. 
57, has been quite successful. This type can be used only where the 




Fig. 53. — Blake-Knowles.jet condenser. 



CONDENSERS 



101 



injection nozzle is less than 18 to 20 ft., above the water supply and 
means must be supplied for priming. 

This arrangement is identical with the jet condenser of Watt and 
the pump may be termed an air pump. Watt's pump consisted of a 
cylinder provided with suction and discharge valves and also a third 
set of valves in the piston and was thus both a lift and force pump. 
Wet air pumps of similar design are common. One set of valves may be 
discarded. The common horizontal air pump is of this type. When 
two of these valve decks are absent the Bodmer, Edwards, or Brown 
pump results and many designs are on the market which give excellent 
service. 



Iniectioa 



Discharge 




///////<'/////y>w//^/////////////M////////ym 



Fig. 54. — Connersville jet condenser. 



These pumps are usually arranged for handling the condensate 
and non-condensible vapors and are known as wet air pumps. 

The development of sugar manufacture showed the need for a pump 
to remove the non-condensible vapors and the air compressor was pressed 
into service for taking these gases at low pressures and compressing them 
to atmospheric pressure. It was found that the volumetric efficiency 
was very low and the Weiss bypass was applied to the air compressor. 
This bypass puts the two ends of the dry air cylinder in communication 
for a short time after the intake and discharge valves are shut and before 
the intake valves open equalizing the pressure on both sides of the piston 



102 



ENGINEERING OF POWER PLANTS 



and avoiding part of the loss due to expansion of the vapor in the clear- 
ance space. 

If the dry air pump works in two stages the bypass is not necessary. 
In these pumps the first stage usually compresses to about twice the 




"Wamm Water Outlet Warm Water Outlet 

Fig. 55. — Counter-current "Rain-type" condenser. 

absolute pressure, leaving the remaining portion to be done in the second 
stage. Not many of these pumps are in service, as they are both costly 
and bulky and the maintenance cost is high, nevertheless attention is 
being called to this type of pump again particularly for the higher vacuum 
work. 

It has been found very difficult in practice to maintain reciprocating 




Fig. 56. — Wheeler rectangular jet condenser. 

dry air pumps tight against leakage. This leakage has in some cases 
amounted to as much as 25 per cent, of the total weight of air to be 
handled which in connection with the bad volumetric efficiency is a 
serious handicap to the maintenance of a good vacuum. 

Reciprocating dry air pumps are quite economical in the use of power. 



CONDENSERS 



103 



The maximum power will be required at about 16 to 17 in. of vacuum 
and decreases as the vacuum improves. 

Where reciprocating dry air pumps are used an air bell should be 



JET CONDENSER 

H.R.WORTHINGTON 



Exhaust Irom Engine 




Fig. 57. — Six types of centrifugal jet condensers. 60,000 lbs. steam condensed per 

hour at 28" vac. 



installed (see ''Air in Surface Condensation/' Transactions A.S.M.E., 
vol. 34). With this apparatus the total air and pump leakage can be 
tested and pumps and condenser shells maintained in good condition. 



104 



ENGINEERING OF POWER PLANTS 



Water-jet air ejectors have long been known and the adaptation 
of these principles to condenser practice is well illustrated in the Koerting, 
Tomlinson and Bulkley ejector condensers. In these condensers the 
air is entrained with the condensate and cooling water and is carried 
away with the water. 




Fig. 58. — Dry-vacuum-pump air cylinder with "Weiss bypass. 

It was due to the Frenchman, Maurice Le Blanc, that these principles 
have been adapted to the abstraction of air from condensers. These 
pumps have three principal parts, a pump to impart pressure to the 
water, an entraining nozzle or nozzles, and a diff user or diffusers, and 
differ only in the arrangement and location of their members. 



Steam 



Suction 




Steam eyluLder Steam Oy Under 

Fig. 59. — C. H. Wheeler suction valveless air pump. 



In the simplest type the pump is separate from the entraining 
nozzle. The pressure water may .be taken from the circulating pump 
or other source and the entraining nozzle and diffuser may be placed 
in the location most convenient to the air eduction nozzle. Such pumps 
are manufactured by the Worthington and Allis-Chalmers Co. in this 



CONDENSERS 



105 



country and by Willans & Robinson in England. The air nozzle 
and diffuser may even be placed inside the condenser as proposed by 
Josse and Gensecke and built by the L. Schwarz A. G. A multiple- 
nozzle pump of this type is made by Koerting. 

Combination units are much more common and the plain cylindrical 
jet and diffuser combined with the centrifugal pump can be obtained. 
A better arrangement, however, is where the entraining nozzle entirely 




Fig. 60. — Sections of Wheeler-Edwards air pump. 



surrounds the runner of the centrifugal pump as in the air pump invented 
by Kolb and improved by Pfleiderer. This pump is manufactured 
by Thyssen in Germany and by the C. H. Wheeler Mfg. Co. in this 
country. Following the same principle but with a widely differing detail 
is the Rees pump made by the Rees Roturbo Mfg. Co. in England and 
by the Manistee Iron Works in America. 

The Kolb pump has a single continuous jet, a continuous entraining 
nozzle and a continuous diffuser, all radial. The Rees type has a single 
jet, a multiple-entraining nozzle and a multiple large-passage diffuser. 

A very interesting and efficient pump built by the A..E. G. in Germany 



106 



ENGINEERING OF POWER PLANTS 




Fig. 61. — Condenser with kinetic air-pump system. 




Fig. 62. — Direct-acting duplex circulating pump, Buffalo Steam Pump Co. 



CONDENSERS 



107 



and by the Wheeler Cond. & Eng. Co. in this country is like both in 
principle, but differs in detail. The jet is broken, the entraining nozzle 
is simple and the diffusers are fewer and converging. This pump is 




Fig. 63. — Condenser auxiliaries, A. E. G. 



used to a large extent in Europe and has given very good service. This 
type may be termed the "slug" type and its action is exactly similar 




Water and Air Pump Circulating Pump Driving Turbine 

Fig. 64. — Section through condenser auxiliaries, Allgemeine Electricitats Gesellschaft, 

Berlin. 



to the Le Blanc pump which has only a single diffuser and a real entrain- 
ing nozzle which is absent in the A. E. G. pump. 

The Le Blanc pump is made in this country by the Westinghouse 



108 



ENGINEERING OF POWER PLANTS 



Electric and Manufacturing Co. and by most all builders abroad. A 
particularly good pump of this type is made by Weir of Glasgow. The 
Le Blanc pump as made by the Westinghouse company is particularly 
adaptable to mixed condensation and many units of this type are in 
service. The Rees pump is also used for this purpose. 




Fig. 65. — Section through diffuser A. E. G. air pump. 

The Kinetic System. — A development of the Parson's augmenter and 
the water-jet pump is the kinetic air-pump system of Richardson, 
Westgarth & Co. Here the air is exhausted from the condenser by the 
steam jet (Parson's augmenter) and delivered to the kinetic ejector which 
takes its water and discharges it into the feed tank. The kinetic ejector 




Section A-A ^ Section B-B 

Fig. 66. — Sections of Westinghouse-Le Blanc air pump. 



is the condenser for the augmenter and also warms the feed water as 
well. This system has many advantages and was installed in con- 
nection with the 25,000-kw. Parsons turbine at the Fiske Street Station 
of the Commonwealth Edison Co. 

It should be remembered that the vacuum obtained by the use of 
water- jet pumps is dependent on the temperature of the water used 



CONDENSERS 



109 



in the jet. Grunewald, in Z.V.D.I., Dec. 7, 1912, has presented a 
most complete set of tests on these pumps measuring the air with nozzles 
and his curves are worthy of careful study. The power used is much 
larger than with the reciprocating pumps because of the large amount of 
water handled. The compression ife nearly isothermal and even large 
amounts of air make little difference in the power. 

The chief advantage of the water-jet pump is the absence of repairs 
and attendance, as it is usually driven by a steam turbine or motor. The 




Infer-cQ/tc/enser 



D/schan^e to Mmospfjere 
ofien Hecrf^r, or Condenser/^ 
Tank 




Fig. 67. 



Fig. 68.— C. H. Wheeler Radojet 
air pump. 



extra power is a small percentage of the whole, although four or five 
times that used by a reciprocating pump. The water for the jet must 
be clean or very carefully strained and in some installations it has been 
especially cooled to secure better vacuums. 

The chief disadvantage of this type is the difficulty of using the air 
bell for determining the air leakage into the system, as the pump diffuser 
usually discharges directly to the discharge tunnel. Discharge wells 
may be provided or a dry air pump installed with piping to each con- 
denser for testing purposes. 

Steam Jet Air Pumps. — The last few years have seen a very rapid 
development in the steam jet air pump by nearly all of the manufacturers 
of condensing apparatus. The use of this type of air pump has become 
almost universal on shipboard and there are a large number of successful 



no 



ENGINEERING OF POWER PLANTS 



installations in land power plants. While a number of different arrange- 
ments of apparatus are in successful use, there are two general types, 

the single or multi-stage 
type without intercondenser 
and the multi-stage jet with 
intercondenser. The simple 
jet without intercondenser 
is very popular for shipboard 
use on account of its light 
weight and extreme simplicity 
of operation. In land service, 
however, the increased effi- 
ciency from the interconden- 
ser which is due to the fact 
that the volume of fluid to be 
handled in the second stage 
is reduced by the elimination 
of the steam from the first 
stage, has led to the installa- 
tion of this type of apparatus 
in a majority of power plants. 
The action of multi-stage 
intercondensing steam jet 
pump is as follows: 

Air is drawn from the 
condenser by a jet of steam 
which delivers the mixture of 
steam and air to a condenser 
which may be of either the jet 
or surface type; the incon- 
densable vapors are then 
caught by a second jet of 
steam and compressed to 
atmosphere. The exhaust 
steam from this last jet is 
available for heating feed 
water. In most installations 
the circulating water for the 
intercondensers is taken from 
the hot well pump discharge 
of the main condenser. 
The principal advantages of this type of air pump are its light weight 
and small size, the absence of any moving parts, its simplicity of opera- 




CONDENSERS 



111 



tion and low power consumption. Fig. 67 and 68 show successful steam 
jet air pumps. 

Hotwells. — Surface condensers should be provided with a hotwell 
so shaped as to retain 
sufficient condensate to 
drown the condensate 
pump. The dehvery of 
this pump may be con- 
trolled by a float. Where 
duplex or triplex pumps 
of the Edwards type are 
used the pipes leading 
to the pumps are usually 
sufficient. 

Priming. — With many 
types of condensers prim- 
ing is necessary to start 
the system. With recipro- 
cating dry air pumps the 
pump may be started and 
a vacuum created in the 
condenser. A pipe con- 
nection with valve be- 
tween the water boxes and 
the condenser will provide 
for the exhaustion of the 
circulating system and the 
water will rise to the cir- 
culating pump which can 
then be started and the 
condenser is ready for 
work. A steam ejector 
applied to the water box 
will perform the same 
service. Water jet vacuum 
pumps are best primed 
from the house service 
lines and after starting 
can exhaust the system 
and raise the water to the 
circulating pumps. 

Expansion Joints. — An expansion joint is usually fitted between the 
condenser and prime mover, and varies in size from the 3 to 6-in. diameter 




112 



ENGINEERING OF POWER PLANTS 




Fig. 71. — ^Thyssen vacuum pump. 




Fig. 72. — Kolb jet condenser and air pump. 



CONDENSERS 



113 



copper joints on very small units to the large 10 by 15-it. joints on a 
30,000-kw. unit. Corrugated copper is largely used for joints of this 
kind, but the best joint is of the Baragwanath type made of steel plate 
which may be welded to the distance pieces. 

This joint has been omitted of late, on very large units and the con- 
denser hung from the steel foundation. In this case smaller expansion 
joints are required in the circulating, air and hotwell connections. 

Power Required for Condenser Pumps. — The power required by the 
air and water pumps connected with condensing apparatus is approxi 
mately 2 to 10 per cent, of the indicated horsepower of the main units. 
J. R. Bibbins {Power, February, 1905) reports for test conditions the 
following figures for a 3,000-kw. plant. 



Indicated horsepower of 
auxiliaries 



151 



200 



238 



260 



291 



294 



457 



589 



Per cent, total power used . 

Per cent, for air pump 

Per cent, for water pump . . 



4.69 
1.63 
3.07 



3.51 
1.36 
2.14 



3.22 
1.27 
1.95 



3.22 
1.21 
2.00 



3.08 
1.19 
1.90 



2.97 
1.09 
1.89 



2.80 
0.95 
1.85 



2.47 
0.85 
1.52 



For a 2,000-kw. turbine at the St. Louis Exposition at full load, the 
power input to auxiliaries was 7 per cent. The 7 per cent, includes 
transformer and motor losses. 



Test of Auxiliaeies of 5,000-Kw. Unit of Boston Edison Co. 



Kilowatts on turbine 

Vacuum 

Barometer 

Boiler-feed pump . . . , 
Circulating pump . . . 
Dry vacuum pump . . 
Step-bearing pump . . 
Wet vacuum pump . . 



Per cent, power of auxiliaries to power of turbine 

Per cent, water used by auxiliaries to that used by 

turbine 



Horsepower developed 




4,756 
28.6 
29.96 



27.4 

69.1 

23.8 

5.6 

9.8 



136.7 
2.1 

5.7 



Finch in the London Electrician, Mar. 22, 1912, gives the following 
figures of the use of power for auxiliaries in English power stations. 



114 



ENGINEERING OF POWER PLANTS 



Location 



Main plant 
kw. rating 



Power used for auxiliaries per cent, of main plant rating 



Feed 
pumps 



Stoker 
economizer 



Fans 



Con- 
denser 
aux. 



Coal 
and 
ash 



Miscel- 
laneous 



Total, 
per 



Chelsea, London 

Carville, Newcastle 

Greenwich, London 

Port Dundas, Glasgow... 

Dunston, Newcastle 

Standreens, Glasgow 

Brighton... 

Stepney • 

Newcastle & District Co. 

Cambridge 

Alnwick , . 

Morpeth 



48,000 

35,000 

34,000 

22,400 

19,000 

16,400 

10,200 

6,000 

5,450 

1,880 

140 

60 



0.5 
0.4 
0.35 



3.3 

2.1 

1.4 
0.8 
4.5 
1.2 
2.2 
0.1 



1.9 
4.1 
3.4 
3.7 
2.6 
7.8 
2.4 
4.9 
4.8 
3.35 

10.0 



0.7 

0.3 

0.7 

0.5 

0.3 

0.5 

0.275 

0.65 

0.1 



1 
5 

45 
3 

7 

275 
4 

45 
55 



4.7 

9.8 

6.1 

8.0 

6.25 

10.5 

9.0 

9.6 

8.7 

6.2 

10.7 

21.0 



He also gives figures for two German stations. 



Hamburg Overhead 
Markische (Berlin) . 



7,900 
7,200 



3.2 

2.2 



0.3 
0.15 



1.25 



2.5 
2.5 



0.0 

0.7 



0.5 
0.2 



7.4 
7.0 



Cost of Condensers. — The average cost of surface condensers with 
pumps is indicated below: 



Engine hp. simple 


Engine hp. 
compound 


Condensers cost 


Erection cost 


Total cost 


40 


50 


$260 


$90 


$350 


60 


100 


380 


125 


505 


100 


120 


490 


160 


650 


120 


150 


540 


175 


715 


150 


200 


610 


200 


810 


200 


250 


670 


230 


900 


250 


325 


775 


250 


1,025 


320 


425 


975 


325 


1,300 



1 



-t^^^ 




i^^^^^^^^^-^^^^^^^^^i:^^^^^^^^^^^ 



Fig. 73. — Ejector air pump inside condenser, L Schwarz A. G., Dortmund, Westphalia. 



CONDENSERS 



115 



From this table it will be noted that the cost of erection is about 33 
per cent, of initial cost. 

The circulating and air pumps are included in the above table. 





Fig. 74.— Willans - M ii 1 1 e r 
ejector air pump 8,500 kw. tur- 
bine, Sheffield, Eng. 



.Discharge 

Fig. 75. — Hydraulic vacuum 
pump, H. R. Worthington, Inc. 



Reducing the above table to cost per horsepower for convenience 
in applying to future estimates the following figures result. 



Engine hp. simple 


Cost per hp. 


Engine hp. compound 


Cost per hp. 


40 


$6.50 


50 


$5.20 




60 


6.43 


100 


3.80 




100 


4.90 


120 


4.08 




120 


4.50 


150 


3.60 




150 


4.07 


200 


3.05 




200 


3.35 


250 


2.68 




250 


3.10 


325 


2.38 




320 


3.04 


4*25 


2.29 





For installations from 500 kw. to 6,000 kw. the cost of various types 
of condensers completely installed is reported as: 



116 ENGINEERING OF POWER PLANTS 

Type Cost per kw. 

Siphon, without air pump $2.00-$3 .00 

Jet 3.00- 4.50 

Barometric with dry air pump 4 . 00- 6 . 00 

Surface for 26-in. vacuum 3 . 50- 5 . 00 

Surface for high vacuum 6 . 00-10 .00 



Cost of Individual Condenser Installations. — A condenser and direct- 
acting pump for a 1,200-hp. installation cost, exclusive of erecting, $2.50 
per horsepower. 

A 1,550-sq. ft. surface condenser for a 750-kw. engine (2 sq. ft. per 
kilowatt); 26-in. vacuum; direct-acting pump underneath condenser and 
centrifugal circulating pump and engine at end of condenser; cost f.o.b. 
factory $2,650 or $3.50 per kw. 

The price of ordinary jet condensers with connecting pipes may 
be taken as from $750 to $2,000 for engines varying from 300 to 2,000 hp. 

Formulae for Cost of Condensers. — An approximate formula that is 
sometimes used for determining the cost of jet condensers is, 
Cost in dollars = 500 -}- 1.0 X hp.. 

Potter {Power, Dec. 30, 1913) gives: 



Type 


Capacity 


Cost $ 


Barometric (28-in. vac.) . 


Up to 30,000 lb. steam per 


1,055+0.112 X (lb. 


steam 




hour. 


cond. hr.) 




Jet (28-in. vac.) 


Up to 30,000 lb. steam per 


1,176+0.1138 X (lb. 


steam 




hour. 


cond. hr.) 




Surface (28-in. vac.) 


Up to 35,000 lb. steam per 


1,630+ 0.2038 X (lb. 


steam 




hour. 


cond. hr.) 




Surface (26-in. vac.) 


Up to 30,000 lb. steam per 


413 +0.1015 X (lb. 


steam 




hour. 


cond. hr.) 





Twenty-eight-inch vacuum surface condensers with pumps cost from 
$1 to $1.80 per square foot of surface depending on price of copper, or 
from $150 to $250 per 1,000 lb. of steam condensed per hour. 

Cooling Ponds. — Where water for condensing is scarce it is found 
economical to store it in reservoirs where it is cooled by evaporation. 
Under the conditions prevailing in northeastern United States it has 
been found that a surface of 250 sq. ft. is sufficient to cool the condens- 
ing water required for a boiler horsepower (34.5 lb.) at 26-in. vacuum. 
In countries where the evaporating coefficient is higher, smaller surfaces 
may be used (see Ruggles, Transactions A.S.M.E., vol. 34, page 561). 



CONDENSERS 



117 



Spray Ponds.— Where the area available for water storage is smaller 
recourse must be had to the spray system. Here the warm condensing 
water is sprayed into the air above the smaller pond ; a portion evaporates, 
cooling the remaining portion which falls to the tank to be used again. 
The sides of the tank are extended to prevent the spray from being 
carried away by the air currents. About 4 sq. ft. of surface are re- 
quired for a boiler horsepower of steam condensed at 26-in. vacuum. 
Such a plant is installed at the power house of the Philadelphia Rapid 
Transit Co. at Second Street and Wyoming Avenue. It is even possible 
in small plants to have the spray pond on the roof of the power house. 




Fig. 76. — Cooling pond, Koerting spray system. 

These ponds should not be used in crowded localities as the spray of 
water is likely to cause a nuisance. The loss of water varies between 
the amount of boiler feed and twice the amount. 

Cooling Towers. — Where the available space is much restricted the 
cooling tower will cool the circulating water to the required temperature. 
The cooling tower consists of a chimney-like structure which may be 
provided with trays, curtains, baffles or gratings. The hot circulating 
water is pumped to the top of the tower where it is sprayed over the 
gratings and allowed to trickle downward to the cold well, exposed to the 
ascending current of air. Natural draft towers depend on the tem- 
perature of the water to produce the air circulation. In the forced draft 
towers this circulation is accelerated by a fan. There are many designs 



118 



ENGINEERING OF POWER PLANTS 




Fig. 77. — Wheeler induced-natural-draft cooling tower, Waco, Texas. 



CONDENSERS 



119 



of these towers on the market but when well designed there is little 
difference in their efficiency. The loss of water is usually from 10 per 
cent, to 20 per cent. With the forced draft towers the fans may use 
from 2 per cent, to 4 per cent, of the output of the main plant. 

Cooling towers and air condensers are quite efficient and can usually 
cool to within 2° to 5° of the wet bulb air temperature. They are rather 
bulky and costly but are quite advantageous when the limit of 
cooling is sufficiently low and their use is demanded by circumstances. 
It should be remembered that a decrease in the lower temperature of 
about 20° corresponds to an increase in capacity of tower of 100 per cent. 




Fig. 78.— Worthington forced-draft cooling tower. 



Cost of Cooling Towers. — Assuming 27-in. vacuum, 70° air and 70 
per cent, humidity, forced-draft cooling towers cost about $250 per 1,000 
lb. of steam condensed. For 24-in. vacuum the cost may be one-half 
this. Natural-draft towers cost about one-half to one-third as much 
as the forced-draft towers. As a general rule cooling towers do not pay 
when the pumping head exceeds 75 ft. 



120 ENGINEERING OF POWER PLANTS 

One writer states the cost of steel cooling towers with fans, complete, 
to be 

Hp. of plant Cost, $ 

500 1,700 

1,000 3,000 

2,000 5,000 

4,000 9,000 

Cost of Water. — Water for condensing purposes, boiler feed, etc., 
may be an expensive item in city power plants. The usual rate for 
water for manufacturing purposes in cities is 40 cts. per 1,000 cu. ft., 
or about 5.35 cts. per 1,000 gal. In New York City this rate is $1 per 
1,000 cu. ft. 



PROBLEMS 

28. Determine the proper design of a condenser for a 1,000-hp. compound condens- 
ing Corhss engine for a nozzle vacuum of 25.8 in. referred to a 30-in. barometer and a 
65°F. circulating water, ^-in. aluminum bronze tubes. 

29. If a new surface condenser is to be installed for the engine of problem 11, how 
many square feet of cooling surface will be required? What would you expect to pay 
for the condenser and pumps, f.o.b. factory? 

30. A 225 kw. D.C. generator is direct connected to a compound, condensing, 
low speed reciprocating steam engine. The load on the generator is as follows: 

Period Hours Kw. 

1 3.0 100 

2 2.0 180 
• 3 2.0 210 

4 1.5 150 

5 2.0 225 

6 1.5 75 

(a) Determine the average total steam consumption of the engine per hour for 
each period. 

(6) What size (No. sq. ft.) surface condenser would you install? 

(c) If wasted to the sewer, what would be the cost of circulating water per day? 

31. The vacuum for a 750-kw. turbo-generator installation is to be furnished by a 
jet condenser. Estimate the pounds of cooling water that will be necessary to give a 
vacuum of 28 in. (30-in. barometer), the injection water temperature being 68°F. 

Could this vacuum be maintained with injection water at 85°F. ? If so, how much 
cooling water would be required? Estimate the cost of the condenser. A bidder 
offers a condenser with a 12-in. exhaust pipe diameter, a 7-in. tail pipe and a 6-in. 
injection pipe. Would you consider this condenser adequate? 

32. Let it be desired to design a condenser for turbine service, 30,000 lb. of steam 
to be condensed per hour, circulating water 70° with a vacuum in the nozzle of 28.4 



CONDENSERS 120a 

in. referred to a 30-in. barometer. Clean salt water for condensing and admiralty 
tubes 1 in. diam. No. 18 BWG. Determine: 

(a) Pounds circulating water per hour. 

(6) Square feet of tube surface. 

(c) Number and length of tubes. 

(d) Size of water connections. 

33. Determine the data called for in problem 25, for a condenser to handle, the 
same amount of steam, the main unit to be in this case a reciprocating engine operating 
under a vacuum at the condenser nozzle of 26 in. referred to a 30-in. barometer. Cir- 
culating water inlet temperature and tubing to be the same as in problem 25. 

34. Determine the relative approximate cost of the following types of engines for a 
unit of 225 hp. 

A. Simple, high-speed, non-condensing. 

B. Compound, high-speed, non-condensing. 

C. Compound, high-speed, condensing. 

D. Simple Corliss, non-condensing. 

E. Compound Corliss, condensing. 
Determine for each type : 

(a) Cost of engine. 

(b) Cost of condenser, air and circulating pumps. 

(c) Cost of foundation, erecting, etc. 

(d) Total cost of engine, etc., erected. 

(e) Probable pounds of steam per hour at rated load. 
(/) Boiler horsepower required for each type. 

35. Same as problem 27 substituting a 450-hp. unit. 

36. Find the same data as in problem 27 for an installation 1,000 hp. divided as 
follows : 

1. Two 500-hp. simple non-condensing Corliss engines. 

2. One 750-hp. compound condensing Corliss engine. 

One 250-hp. compound high-speed non-condensing engine. 

3. One 600-hp. simple condensing Corliss engine. 

One 300-hp. compound condensing high-speed engine. 
One 100-hp. simple non-condensing high-speed engine. 

37. The manager of a small factory is considering the installation of a direct-con- 
nected steam unit of 75-kw. capacity. Two types of engines are under consideration, 
viz., {A) a simple, Corliss, non-condensing; and (B) a compound, high-speed, con- 
densing. He desires to know: 

1. (a) The cost of engine A erected. 

(6) The cost of engine B with condenser erected. 

2. Size of boiler required, 
(a) With type A engine. 
(6) With type B engine. 

3. If all water used is wasted, the cost of water per 308-day year, 11 hr. per day, 
with full load on the engines. 

(a) With type A engine. 
(6) With type B engine. 

38. Determine the items listed below for the following direct-connected A.C. gen- 
erating units, each rated to deliver 600-kw. load. 

A. Compound, high-speed, condensing. 

B, Compound, Corliss, condensing. 
C Condensing turbine. 



1205 ENGINEERING OF POWER PLANTS 

Find for each type : 

(a) Cost of generating unit, 

(h) Cost of condensing equipment. 

(c) Cost of foundations, erecting, etc. 

(d) Total of the above. 

(e) Boiler horsepower required at rated load. 

(/) With steam costing 22 cts. per 1,000 lb., the average cost of steam per 
kw.-hr. if 
(a) Continuous full load is carried; 

(6) Full load is carried for 10 hr. and 40 per cent, of full load is carried 
for 14 hr. 




CHAPTER VI 

THE STEAM BOILER 

There are two conditions governing boiler construction : 
(a) Economy in liberation of energy from the fuel and in genera- 
tion of pressure in the boiler. 

(6) Safety in storage of heat energy. 
Economy may be divided into : 

1. Economy in first cost of boiler and appurtenances and in the 
setting which it may require. 

2. In the combustion of the fuel or in the number of foot-pounds 
of energy derived from the heat units resident in the fuel. 

3. In maintenance and repairs, 
in which would be included depre- 
ciation from use and age. 

The prime requisites of a boiler 
are, first, safety; and second, capacity 
when being driven. 

To meet the condition of "safety 
first," some authorities on boiler 
operation would impose the following Fig. 79.— Egg-ended boiler, 

requirements : 

1. Never use anything but water-tube boilers. 

2. Never use drums greater than 36 in. in diameter. 

3. Always use two valves on all connections to the boiler. 

Types of Boilers. — Formerly boilers were frequently classified as 
externally fired and internally fired, but the commercial classifications 
today are fire-tube and water-tube. 

Fire-tube boilers include: 

(a) Horizontal cylindrical boilers 

(6) Cylindrical-flue boilers. 

(c) Return-tubular boilers. 

(d) Locomotive-type boilers. 

(e) Vertical fire-tube boilers. 

Water-tube boilers include the many types of: 

(/) Sectional boilers. 

(gr) Coil boilers. 

(h) Water-tube boilers. 

The plain cylindrical boiler was the first historically. It must be 

121 



122 



ENGINEERING OF POWER PLANTS 



kept more than half full of water as is also true of all externally fired 
boilers. This type is now used little outside of old plants, in blast-furnace 
practice and in sugar manufacture. Such boilers are very simple, carry 
a large volume of water, steam very steadily after the large mass of 
water is once heated and require little attention. They are, however, 
wasteful of fuel and slow in getting up steam as the heating surface 
is small in proportion to the mass of water. 

Cylindrical-flue Boilers. — The introduction of one or more flues 
(usually 1, 2, 3 or 5) into the plain cylindrical boiler added materially to 
the heating surface, thus shortening the boiler length and at the same 
time extracting the heat from the gases. 




Fig. 80. — Elephant boiler. 

The introduction of these large flues led to the introduction of the 
fire grate into the front end of the flue giving an internally fired boiler. 
The single-flue internally fired boiler is known as the Cornish type. The 
two-flue internally fired is called the Lancashire type. 

Return-tubular Boilers. — Flues are tubes over 6 in. in diameter. 
By a reduction in the diameter and an increase in the number of tubes 
inserted the tubular boiler was developed. The heating surface is thus 
greatly increased and the efficiency of the boiler improved. ''Getting 
up steam" is also much easier than with the plain cylindrical boiler. 
This is the most generally used type of fire-tube boiler. 

In the ordinary fire-tube boiler the tubes are from 2 to 4 in. in diame- 
ter and their usual length is 12 or 16 ft. Locomotive boilers, dry-back 



THE STEAM BOILER 



123 



and Scotch marine boilers and vertical fire-tube boilers are but special 
forms of tubular boilers. 

Water-tube Boilers. — Water-tube boil- 
ers consist of a number of generating 
vessels so joined together that the 
steam formed in all of these separate 
units, or sections, is delivered from a 
common disengagement surface into a 
common steam space. Such boilers are 
also known as sectional boilers and coil 
boilers according to the method of con- 
structing and combining the units. 

Advantages of Sectional Type. — 

1. Each section is far safer against 
rupture than a large shell of the same 
thickness. 

2. Rupture or failure of one section 
does not usually cause failure of the 
whole structure. 

3. Tubes can be thinner than would 
be possible with shells, thus giving a 
lighter weight for a given evaporative 
capacity. 

4. Easy portable. 

5. Repairs and renewals easy, rapid 
and cheap. 

6. Can be driven further above nor- 
mal rating than shell boilers of most 
types. 

Disadvantages of Sectional Type. — • 

1. Units must be connected steam- 
and water-tight. Unequal expansion 
and contraction tend to loosen joints. 

2. Question whether the circulation 
is positive. 

3. Failure of a tube necessitates shut 
down for repairs. Can plug a fire-tube. 

4. Shapes that cannot be properly 
cleaned or inspected are bad. 

5. Gases are liable to pass too rapidly through the system and to 
leave at too high temperature. 

6. Workmanship and parts of sectional boiler make it costly. 

A brief summary of the advantages and disadvantages of the principal 




124 



ENGINEERING OF POWER PLANTS 



types of boilers in commercial use at the present time is as follows: 
Cylindrical-flue Boilers. — > 
Advantages. — 

1 Simple in construction. 

2. Easily cleaned and examined. 

3. Large steam space. 

4. Not liable to prime. 




Fig. 82. — Horizontal-flue boiler. 




Fig. 83. — Section of Lancashire boiler. 



Disadvantages. — 

1. Slow steaming. 

2. Liability to leak from unequal expansion. 

3. Large floor space required. 

4. Specially skilled men required for repairs. 

5. Reduction in pressure necessary after a time. 



THE STEAM BOILER 125 

Return-tubular Boilers. — 

Advantages. — 

1. Small floor space required. 

2. Quick steaming. 

3. Ruptured tubes easily replaced. 

Disadvantages. — 

1. Small steam space, hence pressure liable to fluctuate. 

2. Not easily cleaned or examined. 

3. Liable to leak at end of tubes, at stays and at corners of 
firebox. 

4. Reduction of pressure necessary in time. 

Water-tube Boilers. — 

Advantages. — 

1. Rapid steaming. 

2. Relatively small danger from explosion. 

3. Small floor space required. 

4. Repairs easily made. 

5. Respond readily to changes in steam demand. 

6. Freedom of expansion. 

7. Positive circulation. 

8. Adaptability to high pressures. 

9. Ease of installation. 

10. Elasticity of design. 

11. Large overload capacity. 

12. Reduction of pressure not necessary. 

Disadvantages. — 

1. Small steam space. 

2. Small water reserve. 

3. Large number of parts. 

4. Tubes difficult of access in some types. 

As the majority of the fire-tube boilers already considered are hori- 
zontal boilers, the special advantages and disadvantages of the vertical 
fire-tube types are presented. 

Advantages. — ■ 

1. Light and portable. 

2. Requires no setting. 

3. Rapid steamer. 

4. Takes little floor space. 

5. Upright flow of hot gases is the natural one. 

6. Simplicity of staying, etc., makes it cheap. 



126 ENGINEERING OF POWER PLANTS 

Disadvantages. — 

1. Circulation apt to be defective. 

2. Troublesome to get a dome or large steam space. 

3. Upper ends of tubes not water-cooled in many types and they 
necessarily get very hot, expanding and causing leakage. 

4. Not easy to clean or inspect. 

5. Hold little water. Pass to dangerous pressure quickly. 

6. Strains in certain portions are exceedingly difficult to 
calculate. 

The special features of internally fired boilers are : 

Advantages. — 

1. Economy. Little heat lost by radiation. 

2. On account of 1, the fire rooms should be more comfortable. 

3. Surface is efficient for evaporation, making boilers compact. 

4. Furnace being internal, the boiler requires either no setting 
or one of the simplest description. 

5. No cold air infiltrates through the setting. 

Disadvantages. — 

1. Internal firebox under pressure tending to collapse it inward 
makes it costly. 

2. Efficiency of heating surface keeps temperature of com- 
bustion down and makes smoky products of combustion. 

3. Rapid steaming capacity apt to cause sudden increase in 
pressure, even to the danger point. 

4. Many types hard to clean and inspect. 

5. Circulation not always satisfactory. 

Dependability of the Different Boiler Types.- — 1. All commercial 
boilers will give, under the best conditions, practically the same economy 
in the evaporation of water; a boiler and furnace efficiency of 70 to 80 
per cent, having been obtained with nearly every type of boiler which 
has been tested carefully under good conditions. 

2. The life of all commercial boilers is at least from 15 to 20 years, 
probably much longer. 

3. The only difference between the various types of boilers for 
power-station purposes is the space which they occupy, and the maximum 
rating at which they can be run commercially in everyday service. These 
considerations limit the choice of a boiler for the power station to a very 
few types. 

Materials. — The requisites of boiler materials are sufficient tensile 
strength and a ductility to enable them to withstand strains without 
breaking. 



THE STEAM BOILER 



127 





Galloway Lancashire 

Fig. 84. — Sections of Galloway and Lancashire boilers. 




Fig. 85. — Three-furnace boiler, Lancashire type. 



128 



ENGINEERING OF POWER PLANTS 



Five materials, copper, brass, cast iron, wrought iron and steel 
have been used in boiler construction but as they have all been practically 
forced from the field with the exception of steel, their relative advantages 
and disadvantages need not be presented. 

It is true, however, that copper is still used to some extent for tubes 
for fire engines and for fireboxes in some foreign locomotives; that brass 

is similarly used but seldom found 



Safety Valve Outlet 



Steam ^Outlet Safety Valve Outlet in practice today,* that Cast ITOIl is 

restricted to a few types of low- 
pressure sectional boilers and to 
small parts of larger boilers; that 
wrought iron possesses high tensile 
strength and the necessary tough- 
ness, elasticity and ductility. The 
objection to it is its tendency to 
laminate or blister or both. Very 
little wrought iron is made today, 
so it is seldom found in boiler con- 
struction. Today steel is practic- 
ally the only boiler material in commercial use. 

Specifications for Boiler Construction.^ — The American Society of 
Mechanical Engineers published in 1915 a special report on Standard 




Fig. 86. — Dry-back marine- type boiler. 




Fig. 87. — Scotch marine boiler. 



Specifications for the Construction of Steam Boilers and Other Pres- 
sure Vessels and for Care of Same in Service. A brief summary of 
the points of direct interest in connection with these notes is presented. 
Maximum Pressure. — The pressure allowed on a boiler constructed 
wholly of cast iron shall not exceed 15 lb. per square inch. 

1 For detailed report, see Transactions A.S.M.E., vol. 37, 1916. 



THE STEAM BOILER 129 

The pressure allowed on a boiler, the tubes of which are secured to 
cast- or malleable-iron headers, or which have cast-iron mud drums, 
shall not exceed 160 lb. per square inch. 

Safety Valves. — Each boiler shall have not less than two safety 
valves, one set for the allowed pressure and the other 3 lb. higher. Where 
more than two valves are used on the same boiler (as in cases of operation 
at 300 per cent, of rating), the additional valve or valves should be set 
to blow at 4 or 5 lb. higher than the first valve or valves which start to 
blow at the maximum working pressure allowed. 

Fusible Plugs. — Each boiler shall have one or more fusible plugs. 

Steam Gage. — Each boiler shall have a steam gage connected to the 
steam space of the boiler by a syphon, or equivalent device, sufficiently 
large to fill the gage tube with water,- and in such manner that the steam 
gage cannot be shut off from the boiler except by a cock with T or lever 
handle, which shall be placed on the pipe near the steam gage. The 
connections to the steam gage shall be of brass. 

The dial of the steam gage shall be graduated to not less than one 
and one-half times the maximum pressure allowed on the boiler. 

Each boiler shall be provided with a 3^-in. pipe size connection for 
attaching inspector's test gage when boiler is in service, so that the 
accuracy of the boiler steam gage can be ascertained. 

Water Glass and Gage -cocks.— Each boiler shall have at least one 
water glass, the lowest visible part of which shall be above the fusible 
plug and lowest safe water line. Shut-off valves of the outside screw 
and yoke type are advised in both top and bottom connections to boiler 
to permit of blowing through either independently. 

Each boiler shall have two or more gage-cocks, located within the 
range of the visible length of water glass, when the maximum pressure 
allowed does not exceed 15 lb. per square inch, except when such boiler 
has two water glasses, located not less than 3 ft. apart, on the same 
horizontal line. 

Each boiler shall have three or more gage-cocks, located within the 
range of a visible length of water glass, when the maximum pressure 
allowed exceeds 15 lb. per square inch, except when such boiler has two 
water glasses, located not less than 3 ft. apart on the same horizontal 
line. 

Feed Pipe. — Each boiler shall have a feed pipe fitted with a check 
valve, and also a stop valve or stop-cock between the check valve and 
the boiler, the feed water to discharge below the lowest safe water line. 
Means must be provided for feeding a boiler with water against the 
maximum pressure allowed on the boiler. 

Stop Valve. — Each steam outlet from a boiler (except safety-valve 
connections) shall be fitted with a stop valve. 



130 



ENGINEERING OF POWER PLANTS 



When boilers of 50 hp. or over are set in battery, each boiler shall 

have two stop valves, or a stop valve and stop-cock, on the feed pipe, 

one on each side of the check valve. 

Horsepower Rating. — A boiler having 1 sq. ft. of grate surface shall 

be rated at 3 hp. when the safety valve is set to blow at over 15 lb. 

pressure per square inch. 

A boiler having 2 sq. ft. of grate surface shall be rated at 3 hp. when 

the safety valve is set to blow at 15 lb. pressure per square inch or less. 

Power Ratings for Classification. — 
The horsepower of a boiler shall be 
ascertained upon the basis of 3 hp. 
for each square foot of grate surface, 
if .the boiler is used for heating pur- 
poses exclusively. The engine power 
shall be reckoned upon a basis of a 
mean effective pressure of 40 lb. per 
square inch of piston for a simple en- 
gine; 50 lb. for a condensing engine; 
and 36 lb. for a compound condensing 
engine reckoned upon the area of 
low-pressure piston. The power 
rating of steam turbines shall be 
based on the builders' brake horse- 
power name-plate rating when such 
information is available; or when not 
available and steam turbine is direct- 
connected to electric generating ap- 
paratus shall be taken as the kilowatt 
rating of generator times 1.34. In 
case other suitable means of deter- 
mining rating is lacking the chief of 
the State boiler department may cause 
such investigation as is necessary to 
determine the normal capacity of tur- 
bine to be made, and his decision as 

to rating to be allowed shall be final. 

Boiler Settings. — Internally fired boilers are ready to use as soon as 

located and properly supported (except Cornish and Lancashire and 

dry-back marine). 

Material used for setting boilers is brick. Parts exposed to the 

fierce action of heat should be of firebrick, the rest of common brick. 

Bridge walls and thin parts at front of fireboxes will be of firebrick. 




Fig. 88. — Small vertical boiler. 



THE STEAM BOILER 



131 



The standard mixture for use in boiler settings is usually }i lime and 
% cement. Firebrick are usually set in fire clay. 

If the brick setting is to support the boiler and its contents, it must 
be at least 1}4 bricks (13 in.) thick, and will usually be 17 in. or 21 in. 
for outside walls. The 21 -in. wall is usually made with a 2-in. or 4-in. 
air space between two walls. 

Between boilers in a battery hollow walls are of no value. Such walls 
are usually soHd and 26 in. thick. 

If the boiler is supported 
upon iron framework, the brick 
shell is used to retain the heat 
and gases only. Under these 
conditions the 13-in. solid or 
21-in. wall with air space is used. 

Rear walls if of brick are 
usually solid but rarely over 
12 in. in thickness. 

With water-tube boilers the 
rear brick wall is usually dis- 
placed by steel doors. 

To avoid the infiltration 
of air through cracks in the 
brick setting an air-tight steel 
casing has, in many instances, 
been adopted. The brick walls 
are made thinner, and are 
backed up by 2 in. of mag- 
nesia block and % in. of as- 
bestos board. Outside of this 
a thin steel casing %2 in. to 
J^ in. provided with small 
angles and asbestos packing is 
erected. The steel casing is 
supported by the buck-stays. 

As this casing is held together by small bolts any portion may be Removed 
for repairs to the brickwork or magnesia insulation. Air infiltration is 
prevented and radiation and heat leakage is reduced to a minimum. 

The infiltration of air has been greatly reduced by the painting of 
the boiler setting with a special enamel paint. This paint must not get 
tacky with heat or crack when cold. 

Ample freedom for expansion must be allowed in setting boilers. 
The foundation for a boiler setting may be light if the soil is firm, other- 
wise a substantial foundation must be put in. Such foundations are 




Fig. 89. — Manning boilers. 



132 



ENGINEERING OF POWER PLANTS 



usually of concrete although stone or brick are often used in the smaller 
plants. 

Buck-stays and Tie -rods. — In brick boiler settings it is necessary to 
confine the brickwork to prevent cracking and bulging due to the heat- 




FiG. 90. — ^Locomotive-type boiler. 

ing of the setting. For this purpose it is usual for the boiler manu- 
facturer to supply a set of cast-iron girders which are placed vertically on 
the outside of the setting and tied together with steel tie-rods above 




Fig. 91. — Fairbairn-type internally-fired multitubular boiler. 



the boiler and below the ashpit floor. The cast-iron girders or buck- 
stays are usually spaced about 5 ft. apart and keep the boiler setting 
in shape. Steel has been used instead of cast iron for these buck-stays^ 
especially on the larger and higher boiler settings in which case two 6-in. 



THE STEAM BOILER 133 

channels placed back to back have been used with good success. The 
tie-rods are usually of % in. steel, but should be figured to take care of 
any thrust which the design of the boiler setting may throw on them. 

Hanging or Supporting Boilers. — The ordinary return tubular boiler 
is supported usually on the side walls of the brick setting by means of 
lugs riveted to the boiler shell, slightly above the center line. These 
lugs are supported on round iron rollers to allow for a slight expansion 



Fig. 92. — Babcock & Wilcox-type boiler. 



movement. It is also common to hang boilers of this type, using the 
buck-stays as columns with a supporting beam across their upper ends. 
This makes a much more flexible and secure support and relieves the 
brickwork of many severe strains. 

Practically all of the water-tube types of boilers are hung from an 
overhead structure supported on the buck-stays. The weights are so 
large that the brickwork would have to be inordinately heavy to support 
them. Internally fired boilers of the Manning or dry-back marine types 
are supported directly on the foundations. 



134 



ENGINEERING OF POWER PLANTS 




Fig. 93. — Stirling-type boiler. 
Cost of Fire -tube Boilers. — 



Hp. 


Average size 


Cost f.o.b. 
factory 


Cost per hp,, f.o.b. 
factory 


Cost of 
setting 


Cost of 
boiler set 


Cost set 
per hp. 


50 
60 
70 

80 
100 
125 

150 
175 


54" X 14' 
54" X 16' 
60" X 14' 

60" X 16' 
66" X 16' 
72" X 16' 

78" X 18' 


$485 
565 
620 

700 

850 

1,000 

1,170 
1,310 
1,400 


$9.65 
9.42 

8.85 

8.75 
8.50 
8.00 

7.80 
7.50 
7.06 


$240 
260 
295 

300 
310 
385 

450 
500 
540 


$725 
825 
915 

1,000 
1,160 
1,385 

1,620 
1,820 
1,940 


$14.50 

13.75 
13.10 

12.50 
11.60 
11.10 

10.80 
10.30 


200 




9.70 









THE STEAM BOILER 



135 



These figures may be reduced to the following approximate formulae 
for the cost of horizontal fire-tube boilers. 

Cost f.o.b. factor (I) = 180 + 6.4 X hp. 

Cost of setting ($) = 140 + 2 X hp. 

Other boiler cost figures reported give results considerably below those 
of the formula above, the average of three such formulae being 

f.o.b. cost {%) = 100 + 4.5 X hp. 

One writer gives the cost of settings for fire-tube boilers, exclusive of 
foundations, on the basis of $25 per 1,000 bricks laid. He reports the 
number of bricks required as follows: 



Boiler hp. 


Dimensions 


Brick required 


Fire 


Common 


50 
80 

100 
150 


54 in. X 14 ft. 
60 in. X 16 ft. 
66 in. X 16 ft. 
72 in. X 18 ft. 


1,540 
1,700 
1,880 
2,270 


13,500 
17,300 
19,200 
21,850 




Fig, 94. — Heine-type boiler. 



Cost of Water-tube Boilers. — The following table gives the average 
prices for several different makes of water-tube boilers f.o.b. factory. 



136 



ENGINEERING OF POWER PLANTS 



Hp. 


Total cost 


Cost per hp. 


100 


$1,360 


$13.60 


125 


1,540 


12.30 


150 


1,730 


11.50 


175 


1,950 


11.15 


200 


2,200 


11.00 


250 


2,600 


10.40 


300 


3,100 


10.30 


400 


4,100 


10.20 


500 


5,000 


10.00 



From these figures the following formula is derived : 

Cost f.o.b. factory ($) = 425 + 9 X hp. 

For want of better average figures on price of settings for water- 
tube boilers, the formula for settings for fire-tube boilers may be used, 
viz. : 

Cost of setting ($) = 140 + 2 X hp. 




Fig. 95. — Herreslioff boiler. 



THE STEAM BOILER 



137 



Another estimate for the cost of the brickwork for boiler settings is: 

$3.50-$3.00 per hp. up to 100 hp. 

2.50- 2.00 per hp. up to 200 hp. 

2.00- 1.00 per hp. above 200 hp. 

($1.00 at 500 hp.) 

Potter's formulae {Power, Dec. 30, 1913) — slightly modified — for 
the cost in dollars of the usual sizes of water-tube boilers are: 

For vertical boilers = 900 + 6.3 X hp. 

For horizontal boilers = 150 + 8.2 X hp. 

The following table gives the prices of high-grade water-tube boilers, 
f.o.b. factory in 1916. 




Fig. 96. — Almy water-tube boiler. 



138 ENGINEERING OF POWER PLANTS 

Horizontal Water-tube Boilers with Cast-iron Headers, 160 Lb. Pressure 



Single boiler 

> 


Two in battery 


Hp. each boiler 


Total cost 


Cost per hp. 


Total cost 


Cost per hp. 


200 
300 
400 
500 
600 


$3,000 
4,000 
4,800 
6,000 
7,200 


$15.00 
13.35 
12.00 
12.00 
12.00 


$5,900 
7,750 
9,350 

11,350 


$14.75 
12.90 
11.70 
11.35 



Horizontal Water-tube Boilers with Wrought-steel Headers, 200 Lb. 

Pressure 



Single boiler 


Two in battery 


Hp. each boiler 


Total cost 


Cost per hp. 


Total cost 


Cost per hp. 


200 
300 
400 
500 
600 


$3,900 
5,000 
5,800 
7,050 
8,750 


$19.50 

16.70 
14.50 
14.10 
14.60 


$7,600 

9,600 

11,500 

14,000 


$19.00 
16.00 
14.40 
14.00 



A set of quoted figures for the cost of water-tube boiler installations 
including setting and fittings but not including mechanical stokers or 
economizers, based on the horsepower of compound condensing engines 
is as follows : 



Engine hp. 

400 
600 
800 
1,000 
1,500 
2,000 
4,000 



Cost of boilers 

$ 5,500 
7,500 
9,500 
11,500 
15,500 
20,000 
38,000 



Average Cost of Boilers. — The average cost of boilers including set- 
ting, as reported by one consulting engineer, on the basis of boiler 
capacity required for the indicated horsepower rating of the plant is: 



THE STEAM BOILER 



139 



Cost of Boilers per Engine Horsepower 
(Including Setting) 



Simple non-condensing: 
Engine horsepower. . . . 
Cost per horsepower . . . 



Simple condensing: 
Engine horsepower. . 
Cost per horsepower. 

Engine horsepower. . 
Cost per horsepower. 



Compound condensing: 
Engine horsepower. . . . 
Cost per horsepower. . . 



Engine horsepower. . 
Cost per horsepower. 



10 
$56.00 



10 
$35.50 



40 

$17. 



100 
$8.00 



900 
$6.90 



12 
$51.00 



12 
$33.10 



50 
$15.80 



200 
$7.60 



1,000 
$6.80 



14. 
$46 . 00 



14 

$29 . 60 



75 
$14.80 



300 

$7.40 



1,500 
$6.60 



15 
$43 . 50 



15 
$28.50 



100 
$14.20 



400 
$7.30 



2,000 
$6.40 



20 
$32.00 



20 
$25.10 



500 

$7.25 



30 

$26 . 00 



30 
$20.50 



600 
$7.20 



40 
$24.00 



700 
$7.15 



50 
$20.50 



800 
$7.05 



75 
$17.30 



Weight of Boilers. — The weight of boilers will run approximately 
as follows: 



Type of boiler 


Rated hp. 


Lb. per hp. 


Vertical fire tube ». . . . 


5 

50 

100 
250 


210 


Vertical fire tube '. 


100 


Horizontal fire tube 


135 


Vertical water tube . 


245 


Vertical water tube . . 


175 


Horizontal water tube 


200 







Space Required by Boilers. — Potter gives the floor space and dimen- 
sions of five tube boiler settings as: 



Boiler hp. 


Sq. ft. per 
rated hp. 


Setting dimensions 


50 


2.73 


7 ft. 


7 in. 


X 16 ft. 6 in. X 8 ft. 2 in. high 


75 


2.36 


8 ft. 


10 in. 


X 21 ft. 3 in. X 9 ft. 2 in. high 


100 


2.01 


9 ft. 


6 in. 


X 21 ft. 3 in. X 10 ft. 2 in. high 


125 


1.77 








150 


1.60 


10 ft. 


2 in. 


X 23 ft. 8 in. X 10 ft. 8 in. high 


175 


1.48 








200 


1.38 


lift. 


Oin. 


X 25 ft. 10 in. X 11 ft. in. high 


225 


1.30 








250 


1.22 


11 ft. 


3 in. 


X 25 ft. 10 in. X 11 ft. 2 in. high 



140 ENGINEERING OF POWER PLANTS 

For water-tube boilers he gives 

Boiler hp. Sq. ft. per rated hp. 

150 . 1.62 

625 55 

Cost of Superheaters. — The cost of superheaters seems to run accordini 
to these formulas: 

Cost in dollars (f.o.b.) = 

(For 100°F. superheat) 200 X 2.8 X hp. 

(For 200°F. superheat) 100 X 3.5 X hp. 

(For 300°F. superheat) 75 + 4.5 X hp. 

The cost of erecting is reported as 

Cost of erecting in dollars = 0.5 X hp. 



Furnace Design. — There is no other apparatus in a power plant upon 
which so much depends as the boiler furnace. This is usually the place 
to look for increased economy. Considering the design of the furnace, 
there are three essential features: 

First. — ^A grate must be provided upon which to burn the coal. 

Second. — Means must be provided for the admission of a proper 
amount of air to facilitate combustion. 

Third. — A combustion chamber must be installed, of the proper 
shape and capacity, for the gases which are to be burned. 

Flat grates are used when coal is fired by hand. They may be 
classified as shaking and dumping grates. The shaking grate is best 
adapted for burning coal which has a limited amount of ash, and which 
does not clinker badly. The dumping grate is adapted, as well as any, 
to practically all kinds of fuel, though generally it is more expensive than 
the shaking grate. 

When forced draft is installed, the air is generally admitted in the 
front of the ashpit which forms a chamber large enough to aUow the air 
to come to rest, the pressure in this chamber forcing the air through the 
fire more or less uniformly. When the induced draft system is used, 
the ashpits are left open and the air is drawn in under the grate, or 
through the fire-door, or at any other place where there may be a leak. 



THE STEAM BOILER 



141 



When forced draft is produced by a steam jet — which is frequently used 
in very small installations — it is common practice to place this steam 
jet in the side wall in the ashpit. These steam jets are commonly 
believed by the operating engineers to be especially advantageous on 
account of the prevention of clinker in the ash. This is a very poor 




Fig. 97. — Babcock & Wilcox marine boiler. 



means for preventing clinker, however, as clinker formation is reduced 
because the steam cools the fire below the clinkering temperature. Re- 
cently a combination turbine-driven disk-fan has been used, which is very 
well adapted to these small installations on account of the fact that a 
much less percentage of steam is passed into the grates along with the 
air. The warm air is a great help to the combustion of the coal, but 
few attempts have been made to preheat the air before introducing it 
under the grate. 



142 



ENGINEERING OF POWER PLANTS 



One system which has been used to a small extent, is that of forcing 
the air through passages in the bridge-wall and side walls, but these 
chambers gradually become clogged, and the maintenance expense is 
usually too high to make the advantage derived from the warm air worth 
while. For internally fired boilers the Howden and Ellis-Eaves systems 
are much used in marine practice and also in stationary practice abroad. 
In Howden^s system the air, driven by a fan, is forced through tubes in 
the uptake. Here it is heated and then led into the ashpit and also 
above the grate. The ElHs-Eaves system includes the induced draft 
principle and is usually applied to boilers with larger tubes than the 
Howden system. 

The most important consideration in the design of the furnace is in 
the combustion chamber. The more volatile 
matter the coal contains, the more difficulty this 
problem presents. In burning the fine grades of 
anthracite, it is possible to have the heating sur- 
faces of the boiler relatively close to the grate, 
as practically no hydrocarbons are distilled from 
this coal. With horizontal multitubular boilers, 
the distance from the top of the grate to the 
underside of the boiler is not over 2 to 3 ft., 
and in many cases, under these conditions, this 
coal is burned with fairly good results. When 
soft coal, however, is burned in the same furnace, 
it invariably produces a large amount of smoke, 
and the furnace efficiency is very low. When 
the hydrocarbon content of the coal is distilled 
off, before it can be sufficiently mixed with the 
air to burn, it comes into contact with the sur- 
face of the boiler, and is chilled to a point below 
the combustion temperature. To prevent this, an arch or arches may be 
provided under the shell of the boiler, or the furnace may be built in the 
form of the well-known Dutch oven. A very good setting is produced 
by springing several arches across the grate, between the side walls of 
the boiler, leaving an area between these arches, through which the gases 
may pass, about equal to the area blocked by the arches. 

The height at which the boiler shell should be set above the grate 
depends upon the amount of volatile constituent in the coal. With 
coal containing from 15 to 20 per cent, volatile matter, this distance 
should be not less than 4 to 5 ft. ; and if the coal contains a larger amount 
of volatile matter, this distance should be increased as far as possible. 

The Dutch oven, of course, will produce a better result than the 
construction just described, but it is more expensive to install, and it 




Fig. 98. — Boiler, econ- 
omiser, superheater and 
stoker at the Eberswalde 
Station, Markische E. W. 



THE STEAM BOILER 143 

must be built out in front of the boiler, taking up a considerable amount 
of space. The maintenance is also probably in excess of that of the 
arches. 

When water-tube boilers are installed, the design of the furnace takes 
a somewhat different form. In the first place it is always much wider 
than for fire-tube boilers; and, again, constructive considerations make 
it easier to obtain the required volume for the combustion chamber when 
burning highly volatile coal. In burning fine grades of anthracite, in 
many cases a plain, flat grate only is provided, and this gives fairly good 
results. 

The Webster furnace which has been used in some very large installa- 
tions of late years, is designed, primarily, for burning fine anthracite, 
and has given excellent satisfaction. This furnace consists of four fire- 
brick arches sprung across the grate between the side walls of the boiler, 
their object being to prevent the cooling of the fire when the doors are 
opened for firing. This is a very important matter, especially when 
induced draft is used, as in this case the pressure of the atmosphere is 
anywhere from %o to 1 in. of water above that over the fire; and when 
the doors are open an immense amount of cold air will rush in, chilling the 
tubes and cooling the fire. When forced draft is in use, the difference 
in pressure between the air outside and that over the fire is only sufficient 
to carry away the flue gases, and is seldom over J-f o ^^ %0 i^i- o^ water, 
as the air is forced through the fire by the draft. 

For burning bituminous coal under the water-tube boiler, the number 
of different types of furnaces used is almost infinite. With the boilers of 
the Babcock and Wilcox type, the Murphy furnace — which is essentially 
a Dutch oven — ^is frequently applied, and generally produces good re- 
sults. These boilers are, however, most always used with some form of 
mechanical stoker, and will be considered later. 

The plain Dutch oven is sometimes used, but only on coals of rela- 
tively high volatile content. One of the most effective ways of in- 
creasing the volume of the combustion chamber, and keeping the volatile 
gases from contact with the water surfaces of the Babcock and Wilcox 
type of boiler, is to provide a baffle covering the lower portion of 
the first and second passes, thus circulating the products of combustion 
first over the bridge- wall, thence up through the third pass, down the 
second, and up the first pass to the uptake. This makes possible a 
firebrick roof over the whole grate, extending some 3 or 4 ft. back of the 
bridge-wall, and has all the effect of a Dutch oven without the dis- 
advantages of the latter. The scheme does not require any extension 
front built out from the boiler. 

A very important consideration, irrespective of the type of furnace 
put in, is the height of the boiler tubes above the floor or, what amounts 



144 



ENGINEERING OF POWER PLANTS 





-AE— 




^^^^^^^^^^^^^^^^^ 



f 



^ 



ffRONT ELEVATION 




SECTION ON LINE A.B. 



FiQ. 99. — Setting for flu^h-front boilers. 



THE STEAM BOILER 



145 




Flopy Level \ 




^ 



S 



^— Y— » 



NGITUDINAL SECTIONAL ELEVATION 



3 



1.1.1,1.1 



J_Ji,_Li 



CT I I I 



GE 



III iT^^~n" 



tJid 



I . I . I . I . I . !A .1 . I 



I ' l' .' i'i' ^ 'g^ 



T~n- 



I I I I 1^ 



1.1.1,1,1 .3ZI 



I I I I 1^ 



I . I . I . I I .^ 



-Air Sp acei 



I I I I E 



"T 



rTTTT 



I I I I 



EZE 



T~nT 



1,1,1 



l^TT 



I I I . I- 



I I I I 



13 



I I I I 



'K^ 



GROUND PLAN 



1,1,1,1.1 



I . I . I . I 



zrr 



I I I I I I I I I 



■Air Space i l l 



I I I I I I I I [ 






I I I I 



i 




FRONT ELEVATION i 

FiQ.lOO. — Setting for arch-front boilers. 



K— H — H 

SECTION ON LINE A,B. | \ 



146 



ENGINEERING OF POWER PLANTS 



to the same thing, above the grate. Formerly it was considered customary 
to install the B. & W. boiler with the bottom of its front header about 
7 ft. 6 in. above the floor line. This distance has been gradually in- 
creased for burning the high-volatile bituminous coals, to 9 ft. ; and now, 
in some of the most recent installations, has been made 10 to 12 ft. 
above the floor line. Even this figure might well be increased for burning 
western coals which contain 30 per cent, or more volatile matter. 

Another type of furnace, although not very widely used, for which 
a great deal is claimed, is the Hawley down draft furnace. This con- 




FiG.lOl. — Bigelow-Hornsby boiler. 

sists, essentially, of an ordinary flat grate above which, some 2 ft. or 
more, is a secondary grate composed of tubes through which the boiler 
water circulates. The coal is fed onto this secondary grate. The gases 
are distilled from it here, breaking the coal up and allowing it to fall 
through the bars onto the main grate. The gases from the fresh coal, 
as it is coked on the secondary grate, pass down through the incandescent 
coal which lies underneath, and thence into the combustion chamber. 
Here the gases, which by this time are more or less thoroughly mixed 
with air, are burned by the heat of the burning coke on the main 
grate below. 



THE STEAM BOILER 



147 



In considering the amount of coal which can be burned per square foot 
of grate surface, we find variations under different conditions of from 
12 to 125 lb. per hour. In central-station practice, burning the finer 




Fig. 102. — ^Large Stirling boiler as installed at Hauto, Pa. 



grades of anthracite where forced draft is almost universally employed, it is 
customary to burn, under normal conditions, in the neighborhood of from 
25 to 30 lb. of coal per square foot of grate. On the peak loads by in- 
creasing the draft on the fire, this figure may be, and very often is, in- 



148 ENGINEERING OF POWER PLANTS 

creased to 50 lb. per square foot. The economy when this latter amount 
of coal is burned, is somewhat diminished, due largely to the fact that 
the draft necessary to burn this amount of coal is sufficient to cause a 
certain percentage of it to pass into the back combustion chambers of 
the boilers, and to be deposited in the flues unburned, causing con- 
siderable loss. 

Soft coal is very seldom burned on flat grates in any of the reasonably 
large central power stations, some form of mechanical stoker being em- 
ployed. When soft coal is burned on flat grates, however, it is usually 
customary to burn not over 20 lb. per square foot, as it is very difficult 
with hand-firing, to produce an even distribution of air, and in conse- 
quence, if sufficient time is not given the air to mix with the volatile gases, 
a large part of these will pass off unburned. 

Furnace Losses. — The most serious furnace losses are: 

(a) Heat necessary to create draft. 

(6) Heating air used for combustion. 

(c) Heating ash. 

(c?) Radiation. 

(e) Incomplete combustion, smoke, etc. 

(/) Imperfect transfer of heat. 

Mechanical Stokers. — The Stoker Problem. — In considering whether 
or not mechanical stokers should be installed in a proposed plant many 
technical factors and local conditions must be taken into account. 

The kind of coal to be burned and its cost are important factors. In 
general it may be stated that unless the firemen are expert and exception- 
ally well handled, coal will be burned more economically by using a 
reasonably well-designed mechanical stoker than by the hand-fired 
method. The quality of the labor at hand if not of a good character 
gives added weight to the stoker as it does not require such intelligent 
firemen to handle the stokers properly as it does to fire the coal by hand 
with equal efficiency. The labor problem is also important in the larger 
plants on account of the possibility of strikes. In small plants it is 
always a question whether the saving in labor and coal will warrant the 
investment for stokers. In localities where the finer grades of anthracite, 
such as the buckwheat sizes, are available at a low price it will generally 
be more economical especially in the smaller plants to fire the coal by 
hand. In the larger plants the price of the coal must be weighed care- 
fully against the other conditions previously noted and the decision must 
be made on the merits of the individual case. 

There is one other point which perhaps gives some advantage to hard 
coal and that is when large storage capacity is required. Hard coal may 
be stored in practically unlimited amounts, while it is well known that 
great difficulty due to spontaneous combustion is experienced in storing 



THE STEAM BOILER 



149 



large quantities of bituminous coal especially when it runs high in volatile 
content. A number of plants for the storing of bituminous coal under 
water to prevent loss by spontaneous combustion have been installed. 




Fig. 103. — Green chain-grate stoker under Stirling boiler. 





Fig. 104. — Green chain-grate stoker. 

Types of Stokers. — There are three general types of mechanical stokers, 
although there are several which cannot be conveniently placed in any 
one of these classes. 

The first is the chain-grate stoker consisting of an endless chain placed 



150 



ENGINEERING OF POWER PLANTS 



in the furnace of the boiler with its top side revolving slowly from the 
front of the furnace toward the back. The coal is fed onto this moving 
grate in front and is burned as it passes toward the bridge-wall, where, 
when the grate is moving at its proper speed, the coal will have been 
completely burned to ash which will drop down into the ashpit below. 
Some representative stokers of the chain-grate type are the Babcock and 
Wilcox, the Green, the Playford and the American. 

The second type of stoker is the inclined overfeed type, of which 
the Roney, the Ross, the Murphy and the Wilkinson are examples. 
These stokers consist of movable bars forming an inclined grate with a 




Fig. 105.— No. 1— Type BA7— 22 tuyere, rotary crusher dump Taylor stoker. 



mechanism for moving these bars in such a manner as to cause the coal 
which is fed in at the top to be pushed gradually down the grates until 
it reaches the dumping grate at the bottom, at which point it should 
be completely burned. 

The third type is the underfeed of which the Taylor, the Jones and 
the American are typical examples. In these stokers the coal is fed onto 
the grate or up under the grate in such a manner that the fresh coal is 
always close to the grate while the coal which is being burned is at the 
top. The air is also introduced at the bottom and while passing up 
through the bed of coal is heated and thoroughly mixed with the volatile 
gases distilled from the coal and when passing through the incandescent 



THE STEAM BOILER 



151 



layer at the top reaches its temperature of combustion, so that generally 
no arches are necessary. 

There are several other stokers which are used to a greater or lesser 
extent and work on somewhat different principles, perhaps the most 
notable being the so-called ''finger" stoker which has several oscillating 
paddles which pick up the coal and throw it into the furnace. There is 
another stoker somewhat of this order in which the coal is mechanically 
shovelled into the furnace. These stokers, however, have not reached 
any extensive application as yet and in general are only applicable to 
particular conditions. 

Chain Grates. — The one great advantage of the chain-grate stoker 
over most of the others is that it is suitable for burning with natural draft 




Transv.erse Section 

Fig. 106. — Murphy stoker. 



bituminous coals of very high volatile content. In plants where the 
load is reasonably steady and where sudden peaks are not thrown upon 
the boilers this stoker makes a first-class installation. 

There are two serious troubles with this type of stoker which always 
have to be contended with. The first of these is the leakage around the 
back of the stoker which, in most installations, is very large and cools 
the combustion chamber beyond the point at which volatile gases are 
ignited. This has been obviated to a large extent by certain of the 
manufacturers by placing a long flat arch from the bridge-wall toward 



152 



ENGINEERING OF POWER PLANTS 




Fig, 107. — American underfeed stoker. 




Fig. 108o — Westinghouse underfeed stoker. 



THE STEAM BOILER 153 

the front so that the air which pours up from the back of the chain grate 
will be heated to a sufficient temperature so that it will not cool off the 
combustion chamber. The other trouble which must be looked after 
carefully is the very large percentage of combustible in the ash which 
always occurs with a chain-grate stoker in spite of the fact that the ash- 
pit only covers, in most cases, less than one-third of the area imder the 
grate. 

The method of feeding the coal on to the moving grate varies in the 
different makes. In the Playford and the Babcock and Wilcox stokers 
no feeding device is used, the coal coming from the hopper directly onto 
the grate. In the Green stoker the coal from the hopper is coked on a 
series of movable bars which feed it down onto the chain grate. The 
American stoker has no device for feeding the coal to the chain grate 
but at the bridge-wall end a separate dumping grate is used instead of 
allowing the ashes to merely fall over the end of the grate. The coking 
arches vary but very little in all of these makes, these variations being due 
primarily to the different volatile contents of the coals to be burned. 

Combustion. — The student will find available an unlimited amount 
of good material relating to combustion. One of the most satisfactory 
presentations of this subject is that of H. deB. Parsons in his book on 
''Steam Boilers"^ from which much of the following material is taken. 

''When heat is applied to coal, the resulting combustion is effected as follows: 
first, the absorption of heat; second, the vaporization of the bituminous or hydro- 
carbon portion and its combustion; and third, the combustion of the solid or 
carbonaceous part. These actions are entirely separate and distinct, and must 
take place in the order as given. The hydrocarbon or bituminous portion consists 
of marsh gas, defiant gas, tar, pitch, naphtha, etc. 

The flame is derived from the gaseous portion, and this explains why the soft 
or bituminous coals burn with more flame than the anthracites. 

Coal gas, taken by itself, is not inflammable, as a lighted taper placed in a 
jar of coal gas will be extinguished. In order to consume it oxygen must be sup- 
plied, that is, the gas must be mixed with air. When this is done the gas will be 
consumed instantly, provided the proper temperature be present. 

When a charge of fresh coal is thrown on a fire we cannot control the amount 
of gas that may be generated, but we can control the supply of air. Therefore 
it is essential, when soft coals are to be burned, that a certain amount of air be 
admitted in addition to the regular supply through the grate, during the periods 
of evolution of the gases. This *can be accomplished by permitting air to enter 
above the grate, or directly into the combustion chamber behind the bridge wall, 
or both. The quantity admitted should bear some suitable relation to the per- 
centage of the hydrocarbons contained in the fuel. It is best in all cases to pro- 
vide ample passages for the air, and then to admit the proper quantity as deter- 
mined by trial and observation of the smoke produced. 

In order to burn the coal economically, it has been found necessary that an 

1 "Steam Boilers," by H. deB. Parsons, 4th edition, p. 15. 



154 ENGINEERING OF POWER PLANTS 

excess of air should be allowed to enter the furnace. If only the theoretical 
quantity be supplied, a large proportion of the carbon will either not be con- 
sumed or be only half burned to carbon monoxide (CO). 

On the other hand, too great an excess, as well as a deficiency of air, is a detri- 
ment to the economical working of the furnace. 

Much depends upon the design, especially with soft coals, for the requisite, 
quantity may be supplied in a manner as not to be available; that is, the particles 
of oxygen may not come into contact with particles of carbon. In short, the air 
and particles of fuel may not mix, but rush to the chimney in "stream-lines." 

"The temperature at which some of the physical and chemical changes take 
place when a fresh charge of coal is thrown on a fire are about as follows i^ 

(a) Previous to putting on a charge of coal the temperature of the bed of 
coals is from dull red heat (700°C. or 1,292°F.) up to a bright white heat (1,400°C., 
or 2,552°F.) or even higher. 

(6) The coal, when fired, is about 15°C. or 60°F. (temperature of the room). 
As soon as it reaches a fire-bed it begins to heat by conduction from the hot coals 
beneath. The hot gases, products of combustion of the coal beneath, also heat 
the new charge of coal. 

(c) The heating of the coal causes the volatile matter to distil off. The 
amount distilled at any given temperature is unknown, but it is certain that traces 
of volatile combustible matters are given off as low as 110°C. (220°F.). 

{d) At about 400°C. or 750°F. the coal reaches the temperature of ignition 
and burns to carbon dioxide. 

(e) At about 600°C. or 1,100°F. most of the gases given off by coal (hydrogen, 
marsh gas and other volatile hydrocarbons) will ignite if oxygen be present. 

(/) At 800°C. (1,470°F.) the carbon dioxide, as soon as formed from the coal, 
will give up one atom of its oxygen to burn more coal, thus: CO2 + C = 2C0. 
The carbonic oxide will burn back to carbon dioxide if mixed with oxygen at the 
necessary temperature, which is between 650° and 730°C. (1,200° and 1,350°F.). 

(g) At about 1,000°C. or 1,832°F. the H2O formedby the burning of the hydro- 
gen in the volatile matter in the coal begins to dissociate. 

Qi) At about 1,000°C. or 1,832°F. any carbon dioxide not previously burned 
to carbonic oxide begins to dissociate to carbonic oxide and oxygen. 

(i) The various hydrocarbons which begin to be distilled at 110°C. and possi- 
bly lower, undergo many changes, dissociations and breakings up at the various 
temperatures they pass through. So many of these are unknown that it is use- 
less to state the few we do know. 

About 700°C. (1,300°F.) both the hydrocarbons and the carbonic oxide will 
unite with oxygen if the latter be present and intimately mixed with them. If 
they do not burn, the tendency is always to break up into simpler and more 
volatile compounds as the temperature rises. 

The composition of the gases from combustion may be found in almost any 
ratio. The following volumetric analyses wiU afford some idea of the ratio 
found. The last two are given on the authority of George H. Barrus, the last 
one being the products from Pocahontas (semi-bituminous) coal: 

1 Steam Users' Association, Boston, Circular No. 9, R. S. Hale's Report on Effi- 
ciency of Combustion. 



THE STEAM BOILER 



155 



Poor. 
Per cent. 



Average. 
Per cent. 



Excellent. 
Per cent. 



Carbon dioxide (CO2) 

Oxygen (O) 

Carbon monoxide (CO) 

Nitrogen, vapor of water, etc., by difference. 



8.0 

4.4 

7.6 

80.0 

100.0 



9.0 
11.5 

Trace 
79.5 

100.0 



12.0 
7.5 
0.1 

80.4 

100.0 



15.1 
4.0 
0.7 

80.2 

100.0 



The importance of high CO2 is shown by Fig. 109 taken from a catalogue 
pubHshed by the Westinghouse Company. As stated in this catalogue the 
percentage in the flue gases is a guide as to how well the air is distributed to 
the fuel bed, and whether or not there is 
excess or insufficient air, or an improper 
mixture of air and gases. 

These gas analyses can be made by the 
Orsat or some similar apparatus, by tap- 
ping the flue and extracting a measured 
volume by means of a pressure bottle, 
such as is used in a chemical laboratory, 
and a graduated burette. The sample is 
then forced in succession through three 
pipettes containing caustic potash, pyro- 

gallic acid and caustic potash, and cuprous chloride in hydrochloric acid, which 
will absorb respectively the carbon dioxide, the oxyged and the carbon monoxide. 
The loss of volume at each operation is measured in the burette. 

The refuse from a fuel is that portion which falls into the ashpit and that 
carried off by the draft consisting of ashes, unburnt or partially burnt fuel 
and cinders. 

Loss BY Unburned Coal in Ashpit 



zo 




\M 








Cunes showing the Relative Fuel 
















\\ 








in Flue Gas. Dillmnce beliteen 
Temperatures of En ten ng Air and 
Cxtiaust Gas: 

CurveT=400°Fohr. 
Cun/e~d'=500°Fahr 
CurveT'SOO'Fohr. 


















y 
























^■\ 


\ 




















w. 






\ 


\ 




















^ 


^ 


\ 
































I' 








K 


\ 


\ 




































1 


^ 


V 


\ 


































1 














^ 


Fuel Loss Per Cent 
























~~ 


— - 


-^ 


:n 




^ 


= 


r= 


— 


_ 


_ 




























T 
















/ 





i 





J 





4 





5 





6 




70 


33 


SO 





Fig. 109. 



Remarks — authority 


Per 

cent, 
refuse 


Per cent, 
combustible 
in refuse 


Per cent. 

in total 

coal 


E. B. Coxe {Trans. N. E. Cotton Mfg. Assn., 1895), 


using his 


/ 10.05 

1 23.70 

/ 13.35 

\ 14.31 

16.10 

10.30 

9.20 

18.50 

13.61 

18.70 

8.10 
10.30 
40.00 
14.00 

4.8 


18.68 

11.92 

31.0 

25.0 

25.0 

37.2 

31.3 

29.3 

67.8 

67.2 

26.0 
30.0 
83.0 
51.4 

50.0 


2.2 
2.7 


W. H. Bryan {Trans. A. S. M. E., vol. 16, p. 773), 
coal 


using soft 


4.3 
3 6 


Pennsylvania coal, bars l^i in. wide, 1 in apart. 


4 


Other tests 


3 8 


Other tests 


2.9 


Other tests 


5.4 


Other tests with mechanical stoker 


9.2 


Other tests with mechanical stoker , . - 


12.6 


Arkansas State Geological Survey Report, 1888, vol 


3, p. 73, 


2 1 


Ditto Arkansas coal 


3.1 


Ditto Arkansas coal 


33.2 


Ditto Arkansas coal 


7.2 


Dampfkessel Revision Verein Berlin Geschafts Bericht, 1895, 
p. 79. Coal dust 


2.4 







156 ENGINEERING OF POWER PLANTS 

The following is from a report of R. S. Hale, Steam Users' Association, Boston, 
Circular No. 9: 

''The amount of loss by unburned coal in the ashpit depends on so many 
factors that it is impracticable to express it by any formula. A statement of 
the factors and a collection of examples must, therefore, suffice. 

(a) The loss by unburned coal in the ashpit depends on the width of the open- 
ing in the grate bars, and increases as the width increases. 

(6) The loss depends on the size of the coal, and increases as the size of the 
coal decreases. 

(c) The loss is probably greater for a non-caking than for a caking coal. 

{d) The loss probably increases as the amount of earthy matter in the coal 
increases, but not the same ratio. 

{fiY The loss is less with a fan blast than with a steam blast. 

(/)2 The loss is greater the more the fire is disturbed. This is especially 
noticeable in automatic stokers with moving grate bars." 

The following formula of Dulong is convenient for determining the theoretical 
quantity of air that is required for the combustion of any fuel whose composition 
is known. 

Let C, H and O denote respectively the weight of carbon, hydrogen and oxygen 
in the fuel; and W and V the weight and volume of air required. Other ingredi- 
ents may be neglected, as they have but a slight effect on the result. Then 

W = 11.610 + 34.78 (h - ^) , or 

W = 120 + 35 (h - ^) , nearly; and 

V = 152.560 + 457.04 /h - ^) , or 
0^ 



V - 1530 + 457 (h - g) , nearly. 



The value of W per pound is about 12 for anthracite and good bituminous 
coals, 6 for wood, and 11 for charcoal. 

It is found impossible in practice to obtain complete combustion unless the 
air supplied to the furnace be in excess of that theoretically required. Experience 
dictates that for ordinary natural draft nearly twice the theoretical quantity of 
air should be admitted, or about 24 lb. per pound of coal. With mechanical 
drafts and with natural drafts when the mixing effects are strong and positive, 
the excess of air may be considerably reduced. 

The volume of air supply per pound of coal, in ordinary factory practice, with 
natural draft is about 300 cu. ft. ; and may be as low as 200 cu. ft. when the mixing 
effect is strong." 

The actual volume may be estimated by using an anemometer, or may be 
closely calculated from a flue gas analysis by using the following formula. 



A = 11.6 



00 



002 + ^+02 Q 

. OO2 + OO ~ X O + 3(h - gj 



1 Report of Coal Waste Commission, Pa., 1893, p. 31. 

2 Report of Coal Waste Commission, Pa., 1893, p. 31. 



THE STEAM BOILER 157 

where 

A = weight of dry air per pound of dry coal; 

CO2, CO, and O2 = per cent, volume of each in the flue gas; 

C, H and O = the weight of each in 1 lb. of dry coal. 
The total weight of the dry products of combustion passing out of the stack 
will be 

w. = c X (,1 + 11.6— ^oT+'co-/ + '^-'F - 8/ + ^ 

or, expressed in terms of '*A/' above 

Wi = A + C+N -8(h -|) 

where 

Wi = total weight of dry combustion products per pound of dry coal; 
N = the weight of nitrogen in 1 lb. of dry coal. 
The specific heat of the dry flue gas may be taken at 0.24 for ordinary purposes 
of calculation of B.t.u. loss. 

The loss due to an incomplete combustion of the carbon to CO will be, in units 
of B.t.u. loss per pound of fuel, 

^ ^ . „ ^ 10,16QXC O 

B.t.u. loss = C X C02 + C0~' 

"The conclusions drawn by R. S. Hale^ are: that ordinary firing is apt to give 
10 to 20 per cent, worse results than the best skilled firing, the low results being 
caused by using too much air and by getting poor combustion. 

That it is easier for firemen to get better results in some boiler furnaces than 
others, but that this difference becomes large only with poor soft coal. 

That many but not all of the patent devices (down-draft grates, stokers, 
etc.) in common use will with moderately skilled firemen give better results than 
those obtained by ordinary firemen in ordinary furnaces. 

That it is probable, but not proved, that ordinary firemen can get better re- 
sults from these devices than can ordinary firemen on ordinary grates. 

Heat of Combustion. —The heat produced by the combustion of 1 lb. of various 
substances is given in the following table in British thermal units: 

Total Heats of Combustion 

B.t.u. per lb. 

Hydrogen 62,032 

Carbon to carbon dioxide 14,500 

Carbon to carbon monoxide 4,400 

Carbon monoxide to carbon dioxide 4,330 

Olefiant gas. 21,344 

Liquid hydrocarbons vary in proportion to weight from 19,000 

to. 22,600 

Charcoal, wood 13,500 

Charcoal, peat 11,600 

Wood, dry, average 7,800 

Wood, 20 per cent, moisture , 6,500 

Peat, dry, average 9,950 

^Steam IJgers' Circular, No. 9. 



158 ENGINEERING OF POWER PLANTS 

Peat, 25 per cent, moisture 7,000 

Coal, anthracite, best qualities, about . 15,000 

Coal, anthracite, ordinary, about 13,000 

Coal, bituminous, dry, about 14,000 

Coal, cannel, about 15,000 

Coal, ordinary poor grades, about , 10,000 

These figures are slightly altered by different authors. The above list may 
fairly be taken as an average." 

Boiler Rating. — It has been customary in the past to rate fire-tube 
boilers at 11.5 sq. ft. of heating surface per horsepower, water-tube boilers 
at 10 sq. ft. of heating surface, and internally fired boilers at 8.5 sq. ft. 
of heating surface per horsepower, a horsepower being understood to be 
the ''Centennial rating," 343^ lb. of water evaporated per hour from and 
at 212°F. This rating is in use today, but most engineers buy square feet 
of heating surface and not horsepower, this being due to the great 
advances which have been made in the art of firing boilers. At the time 
of the formulation of the ''Centennial rating" 3.5 lb. of evaporation per 
square foot of surface per hour was considered very good work and the 
economical point of evaporation. At the present time with better designed 
boilers and our better knowledge of combustion problems it is not uncom- 
mon to obtain 9 or 10 lb. of evaporation, with gOod economy, from large- 
tube boilers and as much as 15 to 18 lb. with the smaller tube types. Prof. 
Bone, with his surface combustion boiler, has evaporated from 30 to 
45 lb. of water per square foot of surface per hour over a considerable time, 
with excellent economy. 

Considerable discussion has arisen regarding the measurement of 
heating surface, i.e., whether such measurements should be based on 
the inside or outside diameters of the tubes. 

The American Society of Mechanical Engineers favors using the 
surfaces which receive the heat — the outside diameter of water-tube 
and the inside diameter of fire-tube boilers. 

Boiler and Furnace Efficiency. — Boiler efficiency may be graded as 
follows: 50 to 60 per cent, poor; 60 to 70 per cent, fair; 70 to 75 per cent, 
good; over 75 per cent, excellent. The last is seldom obtained. 

Tests of very large boilers (approximately 24,000 sq. ft. of heating 
surface) have shown remarkable efficiencies of 

80 per cent, at 93 per cent, rating, 
and 76 per cent, at 214 per cent, rating. 

It should not be forgotten that the efficiency is materially effected 
by scale. Scale 3^^ in. in thickness may cause a heat loss of 10 to 12 per 



THE STEAM BOILER 



159 



cent. A thin film of grease is, however, more harmful than a fairly 
thick scale of carbonate of lime. 

The effect of heat loss is perhaps best shown by Figs. 110 to 113, the 
percentages being those given by Kreisinger.^ 




Fig. 110. — The average boiler-plant Fig. 111. — The best plants are doing 

does like this. like this. 




Fig. 112. — The average plant can and should do like this. 




Fig. 113. — Where the heat goes in the average boiler-plant. 



1 "Saving Coal in Boiler Plants," The Universal Engineer (New York, Feb., 1919) 
by Henry Kreisinger, Engineer U. S. Bureau of Mines. 



160 ENGINEERING OF POWER PLANTS 

Following the general discussion of boiler efficiencies by Maguire:^ 

Let w = equivalent evaporation per pound of coal as fired. 
m = percentage of moisture in coal. 
a = percentage of ash by analysis. 
a^ = percentage of ash and refuse (from test) in terms of coal 

fired. 
He = B.t.u. per pound of combustible. 



then 



and 



boiler efficiency = 
boiler and furnace efficiency = 



970 X w 



He (100 - m - a') 

970 X w 

H, (100 - m - a) 



The two efficiencies will be the same when a^ = a. For solid fuels 
the difference between a^ and a gives a line on the grate or stoker effi- 
ciency. For liquid or gaseous fuels a^ = a = 0. 

For good operating conditions with boiler and furnace adapted to the 
requirements and with the plant operating at normal rating, the following 
boiler efficiencies should be expected for the coals indicated. 





Moisture, 
per cent. 


Ash, 
per cent. 


B.t.u. per 
lb. comb. 


Refuse 
from test, 
per cent. ' 


Boiler 

efficiency, 
per cent. 


1. Eastern semi-bituminous and 












bituminous coals of 13,000 












B.t.u. per lb. day 


4 


10 


14,500 


12 


72 


2. Eastern semi-bituminous and 












bituminous coals of 13,500 












B t u per lb. day 


2 


7 


14,540 


9 


73 


3. Western bituminous coals of 












12,000 B.t.u. per lb. dry 


8 


15 


14,300 


20 


65 


4. Western bituminous coals of 












11,000 B.t.u. per lb. dry 


12 


20 


14,200 


23 


62 


5. Anthracite buckwheat No. 2 of 












12,000 B.t.u. per lb. dry 


5 


16 


14,400 


20 


68 


6. Anthracite buckwheat No. 3 of 












11,000 B.t.u. per lb. dry 


5 


25 ■ 


14,800 


28 


65 



The relations between efficiency and capacity and between capacity 
and flue-gas temperature are shown in Fig. 114. 

1 "Boiler Efficiencies for Various Coals," by T. F. J. Maguiee, Engineering Maga- 
zine, Vol. XXXVllI, p. 330. 



THE STEAM BOILER 



161 



Pounds of Water per Horsepower-hour.- — James Watt's figure was 1 
cu. ft., or 62.5 lb. The standard of 1876, Centennial, adopted by the 
American Society of Mechanical Engineers was 30 lb. evaporated from a 
temperature of 100°F. (feed water) into steam at 70 lb. gage pressure. 

This is equivalent to 34.5 lb. from and at 212°F. 

As has already been pointed out there is no direct relation between 
boiler and engine horsepower. 



75 
70 
G5 
60 
55 
50 
& 45 
« 40 













h-^~ 






























1 


ffic 


enc 


7^ 


"v. 
















700 


















^ 


^ 


































V, 


V, 


































^ 


V 


-I 

-0" 






























S 


GOO 


























































^ 


a 

a) 






















^ 




T 






H 

— c§- 

O 

— <D- 


















^ 


^ 


^ 


le 


3as 


















/ 


V' 




^ 


Cem 


per 


atu 


re 




500 










/ 


/ 




























/ 


r 




























/ 


f 




























/ 


/ 






























/ 




























lOO 































100 150 200 

Percent Capacity 



250 



Fig. 114. — Relation of efficiency, flue gas temperature and per cent, capacity. 



For convenience in comparing the evaporative results of boilers operat- 
ing under different conditions of feed-water temperature and steam 
pressure, it is necessary to reduce all such variable conditions to a defi- 
nite standard. The conditions agreed upon, which have been in use 
many years, are those of a feed-water temperature of 212°F. and the 
evaporation of the water at that temperature into steam at atmospheric 
pressure, with a temperature of 212°F. This has been shortened into 
either "Equivalent evaporation'' or "Evaporation from and at 212°.'' 

Factor of Evaporation. — At the pressure of one atmosphere (14.7 lb. 
per square inch) and at 212°F., the heat necessary to make water at 
that temperature into steam at that pressure is approximately 970 
B.t.u. 

If, then, the total heat, Q, required to vaporize a weight of water, 
TF, be observed from a test, in which the feed water was introduced at 
t' ^ and the evaporation took place into steam at t, the total heat which 
went into the evaporated water was the product Q X TF. 



162 ENGINEERING OF POWER PLANTS 

If the evaporation had taken place from and at 212°F. Q would 
have been 970 for each pound, so that 970^/" would have been the equiva- 
lent heat absorbed if H is the corresponding weight of water evaporated 
from and at 212°F. 

Equating these, ^^ 

QW = 970H orH = ^ 

gives the pounds of water which would have been evaporated from and 
at 212°. ^ 

A table giving the value of the factor x^ has been computed and 

may be found in various books dealing with boiler tests. This factor 
is designated, "Factor of Evaporation." 

For example, given feed water at 40°F. evaporated into steam at 
100 lb. gage, what is the factor of evaporation? 

If g = the heat of the hqm'd at 40°F. = 8.1 
qi = the heat of the liquid at 100 lb. gage (338°F.) = 309 
r = the heat of vaporization at 100 lb. gage = 879.5 
then gi - g = 309 - 8.1 = 301 
then total heat = 301 + 879.5 = 1,180.5 B.t.u. per pound 

' -p^' = 1.22 = factor of evaporation, that is, the evapora- 
tion of 1 lb. of water from a feed-water temperature of 40°F. into steam 
at 100 lb. gage pressure is equivalent to evaporating 1.22 lb. from water 
at 212°F. into steam at 212°F. 

The average factor of evaporation for the wide range of feed-water 
temperatures and steam pressures in common use is roughly 1.15. 
This approximate factor may be used for all general calculations that 
do not require close refinement. This corresponds to the evaporation 
of 30 lb. of water per horsepower-hour under ordinary commercial 

34 5 
conditions as tt^ = 30. 
1.15 

Pounds of Water Evaporated per Pound of Dry Coal (from and at 

212°).— 

Maximum theoretical 15 

Maximum under conditions of practice 12 

Excellent practice 10 

Fair practice 8 

Common practice (small plants) 7 

From the formula for boiler efficiency the following equivalent 
evaporations are obtained: 



THE STEAM BOILER 



163 



Coal No. 


Boiler and furnace 
efficiency, per cent. 


Equivalent evaporation per 


lb. of 


Coal as fired 


Dry coal 


Combustible 
burned 


1 


70.3 


9.04 


9.41 


10.70 


2 


71.4 


9.74 


9.96 


10.92 


3 


60.8 


6.90 


7.50 


9.38 


4 


59.3 


5.90 


6.71 


8.72 


5 


64.6 


7.56 


7.95 


9.94 


6 


62.2 


6.63 


6.99 


9.70 



In a similar way expected equivalent evaporations and boiler and 
furnace efficiencies may be deduced for any given fuel. (See Prob. 43.) 

Pounds of Coal per Square Foot of Grate Area per Hour. — 

(a) With chimney draft: 

Slowest rate, Cornish boilers 4- 6 

Ordinary rate, Cornish boilers 10- 15 

Ordinary rate for anthracite 15- 20 

Ordinary rate for bituminous 20- 25 

(6) With forced draft: 

Stationary water-tube boilers . ; 25- 50 

Locomotives 40-100 

Torpedo boats 60-125 

Boiler Deterioration. — Boilers are subject to many deteriorating 
forces which may be summed up as: 

(a) Internal corrosion. 

(6) External corrosion. 

(c) Pitting. 

{d) Grooving. 

(e) General wear and tear. 

Idle Boilers. — When boilers are out of service for any length of time 
they should receive the following treatment as specified by Parsons. 

*' The outside should be cleaned and painted with a good metallic paint, 
applied directly to the cleaned and dried surface. If the boiler be covered by 
lagging, the lagging should not be allowed to absorb moisture from the atmosphere. 

On the fire side, the soot and ashes should be thoroughly removed and the 
surface cleaned. These surfaces should then be kept dry and not exposed to 
damp air. Fresh lime in pans or trays, renewed as required, will absorb the 
moisture in the air. Occasional small fires of tarred wood will be beneficial, as 
the heat will dry the metallic surfaces and the resinous condensations from the 
thick smoke will cover the tubes and shell with a protective coating. 

On the water side, corrosion may be active at the water line if the boiler be 
left partly full. Idle boilers should, therefore, be entirely dry or completely 



163a ENGINEERING OF POWER PLANTS 

filled with water. If the laying off is a short time only, it is a good plan to fill 
the boiler with water made alkaline by a little soda. If for a long period, it 
seems best to empty the boiler and dry out the inside by a small fire built in a 
pan, which can be inserted through the lowest manhole. The manhole and hand- 
hole covers can be put back and the boiler made tight so that the oxygen will be 
consumed by the fire, or the covers can be left off and lime in trays used to absorb 
any moisture. 

Boiler Explosions. — Parsons states that explosions occur when the 
steam pressure exceeds the resisting strength of the metal structure. 

In a well-designed boiler the parts are of approximately equal strength 
throughout. It is good practice so to design a boiler that those parts 
shall have an excess of strength which are expected to suffer most rapidly 
from corrosion or wear and tear. Then as the boiler advances in age, 
the various parts become more nearly equal in strength. 

Should a boiler become weakened and a rent occur, the steam pressure 
will be suddenly reduced, thus releasing the heat stored in the water. 
A portion of the water instantly flashing into vapor probably accounts 
for the great destructive effects produced by an explosion. 

While the rent primarily occurs at some weak spot, the fracture may 
not and seldom does follow a line of structural weakness. The new forces 
set up at the instant of explosion no doubt account for this phenomenon. 

All things being equal, the damaging effect by explosion of water- 
tubular boilers will be less than of fire-tubular boilers of equal rating, 
since the former contain a smaller proportion of water, and since extra 
time will be required for complete release, because the bursting part is 
small. 

Failures of boilers are usually due to wear and tear, produced chiefly 
by expansion and contraction, to corrosion, to overheating and to care- 
lessness. Overheating may be caused by low water or by scale or grease. 
Important fixtures, such as main stop valves, may become attacked, or the 
main steam pipe may be burst by water-hammer, thus causing a sudden 
release of pressure, which, if quick enough, may be followed by an 
explosion. 

When an explosion does occur, it is frequently difficult to determine the 
cause, and hasty judgment should always be withheld. A good piece of 
metal may show a poor quality of fracture on account of the suddenness 
of the rupture. Opinion as to the quality of the metal should only be 
given after a close and careful analysis of physical and chemical tests. 

The best way to prevent explosion is to employ intelligent labor and 
not neglect proper and regular inspection." 

Boiler Inspection. — The requirements and regulations regarding 
inspection are given in the American Society of Mechanical Engineers' 
Code. 



THE STEAM BOILER 1636 

Number of Boilers to do Given Work.-^The subdivision of heating 
surface into the proper number of boilers is important, for a careful study- 
may result in much saving in first cost and in cost of operation. 

For instance, if boiler capacity to evaporate 33,600 lb. of water per 
hour from and at 212° is required, approximately 9,600 sq. ft. of heating 
surface will be needed. 

If each square foot of heating surface may be overloaded 33 J^ per 
cent, (which is quite possible in ordinary practice) it is evident that if the 
9,600 sq. ft. were divided among four boilers, one boiler might be shut 
down for repairs or cleaning, and the other three run at 333^3 per cent, 
overload and still evaporate 33,600 lb. of water. 

If the total heating surface were divided into three boilers, each of 
3,200 sq. ft. of heating surface, two might not be able to run the plant 
alone, so a fourth or spare boiler would have to be supplied. This would 
be poor division of power as the money spent on the spare boiler would 
represent so much capital lying idle most of the time. 

Selection of Boiler Type. — The choice of type will depend much upon 
the conditions of service. 

For high pressures such as are used for modern power plants, water- 
tube boilers are safer. They are also probably more economical and 
meet the varying demands better than fire-tube boilers. 

For reasonably low pressures in relatively small power plants and for 
heating installations the ordinary fire-tube boiler meets the requirements 
well if overload capacity is not an essential factor. Such boilers are 
cheaper and probably cost less for repairs than water-tube boilers. 

The tendency with fire-tube boilers is toward hand-fired furnaces, 
which are often objectionable because of excessive smoke production 
which may make them undesirable for urban conditions. 

Saving by Use of Mechanical Stokers. — The difference between good 
and bad firing may easily amount to from 5 to 20 per cent, of the amount 
of fuel fired; hence, there is no investment around a steam plant which 
will pay better than the extra amount paid to secure good boiler practice. 

Automatic stokers are now developed to a remarkable degree of per- 
fection, and when suited to the fuel have an advantage over hand-firing 
in that under all conditions they are reliable, can be adjusted to the 
minimum of air and the maximum of load, and can be depended upon 
to operate continuously with the minimum amount of skilled labor. The 
economic saving will depend on the basis of comparison and the method 
of operation. Compared with an ordinary or poor fireman, they should 
show a large saving. Whether a stoker will save labor in the fire room 
depends upon the size of the plant. As a rule, mechanical stokers are 
not labor-saving devices in plants containing less than six to eight boilers 
(1,500 to 4,800 hp.). 



164 ENGINEERING OF POWER PLANTS 

One man can handle the coal and ashes, fire the boilers and attend to 
the water level of 200 hp. of boilers equipped with the common hand- 
fired furnace. With shaking or dumping grates 300 hp. may be con- 
trolled by one man. With large boilers equipped with dumping grates 
one man will fire around 1,000 boiler hp. when using the steam sizes of 
anthracite coal, but the coal must be delivered in front of the boiler and 
a water tender is usually provided for every 24 boilers. With soft coal 
about 700 boiler hp. may be fired by one man under similar cirumstances. 
In a large plant containing twelve 650 B. & W. boilers, equipped with 
stokers, a water tender, one fireman and one helper are required per 
watch for their efficient operation. In stations of this size the ash men 
are in the basement, and the change from hand- to stoker-firing would 
make no difference in their number. 

One authority states that stokers save 30 to 40 per cent, of the boiler 
labor in plants using over 200 tons of coal per week; 20 to 30 per cent, 
in plants using from 50 to 200 tons of coal per week, and no saving in 
plants below 50 tons. 

It should be remembered that unless the type of stoker is suited to 
the kind of fuel obtainable, the maintenance of the stoker plant is likely 
to be extremely high, running in some cases twice or three times as high 
as fire-room labor under hand-fired conditions. 

Cost of Mechanical Stokers. — In general, mechanical stokers cost 
from $3.50 to $6.50 per boiler horsepower, but the cost depends more 
on the width of the stoker than on the horsepower of the boiler. Chain- 
grate stokers cost in the neighborhood of from $180 to $250 per foot of 
width. Inclined-grate stokers of the Roney, Acme, Wilkinson or similar 
types, from $140 to $225 per foot of width. Underfeed stokers from 
$200 to $300 per foot of width. The length of the stokers is usually 
standard and depends on the type of coal to be burned. These prices 
differ considerably with the amount of auxiliary material furnished 
with the stoker, such as fronts, air boxes, coking arches, stoker drives and 
speed-changing devices, but are based on labor and material costs current 
in New York prior to the European war. 

The following is the approximate cost of stokers suitable for a water- 
tube boiler of 350-hp. rated capacity with 45 sq. it. of grate surface; 
height of chimney above grate, 175 ft.; coal burned, Illinois screenings. 
The cost of the installation is not included. 

1. Burke smokeless furnace 1,000 

2. Wilkinson stoker 1,200 

3. Roney stoker 1,300 

4. Hawley down-draft furnace 1,350 

5. Murphy furnace and stoker 1,350 

6. Jones underfeed stoker 1,400 

7. Chain grate and appurtenances 1,500 

8. Taylor stoker 2,000 



THE STEAM BOILER 



165 



R. J. S. Pigott {Proceedings Am. Elec. Ry. Assoc, 1914) gives the 
following data for mechanical stokers. 

Average Data for Stokers 



Type of stoker 



Step and 

slope 
overfeed 



V 
over- 
feed 



Chain 
over- 
feed 



Gravity 
under- 
feed 



Horizontal 

retort 
underfeed 



Average price per rated boiler horsepower 
Normal forcing ability in per cent, of rating 
Price per raaximum horsepower develop- 
able 

Maintenance per ton coal fired, in cents. . . 

Attendance in man-hours per active hour. 

Pounds coal per square foot grate surface 

(maximum) 



$3.60 
190 

$1.90 

10-12 

0.45 

35-38 



$3.60 
175 

$2.06 

11-14 

0.45-0.50 

35-42 



$3.50-$6.55 
260 

$2.52 

6-10 

0.20-0.30 

45-48 



$5.65 
300-350 

$1.62-$1.88 

2.5-4 

0.08-0.10 

60-75 



$4.44 
300 

$1.48 

4-6 

0.30-0.40 

50-65 



Operation and Care of Boilers. — Full instructions regarding the opera- 
tion and care of steam boilers will be found in the Code published by The 
American Society of Mechanical Engineers (1916). 

Among the most important points upon which the power plant 
engineer should be informed are* 



(a) Water level. 




Qi) Blowing off. 


(6) Leaks. 




(i) Grease. 


(c) Getting up steam. 




0") Efficient operation. 


{d) Cutting in boilers. 




ik) Banking fires. 


(e) Low water. 




(Z) Scale prevention. 


(/) Foaming. 




(m) Shutting down. 


{g) Safety valves. 




(n) Inspection and repairs. 




(o) Laying up 


boilers. 



PRINCIPAL LOSSES IN BOILER-PLANT OPERATION 

As pointed out by the United • States Fuel Administration, the chief 
losses in boiler-plant operation are: 

Cause Remedy 

1. Dirty boiler — loss up to 25 per cent Clean boiler. 

2. Leaky setting — loss up to 15 per cent Tight setting. 

3. Poor firing — loss up to 40 per cent Good firing. 

1. A boiler may be dirty on the inside or outside or both. Dirt 
on the inside is due to scale formation and can be corrected by clean- 
ing the boiler and then giving consideration to the character of the 
feed water and its proper treatment. See Engineering Bulletin No. 3 
of United States Fuel Administration. 

Outside cleaning must receive careful attention. A slight accumu- 
lation of soot deposited in a few hours' run will result in a growing 
loss of efficiency. Some one must be delegated to follow up this matter 
of soot and see that the cleaning is done thoroughly, frequently, and 
regularly. 



165a ENGINEERING OF POWER PLANTS 

2. Air leaks reduce efficiency. The ordinary brickwork setting 
develops cracks and crevices which allow a considerable amount of 
air to enter the setting, lowering the temperature of the gases of com- 
bustion. The porous character of the brick itself is such that an appre- 
ciable leakage takes place through the walls. 

The remedy is to point up the brickwork with plastic fireproof mixture 
and paint or cover the setting with a coat of air-tight material. 

3. Bad firing includes allowing holes to develop in fuel bed; carry- 
ing an uneven fire ; carrying too thin a fire ; carrying too thick a fire ; stir- 
ring fire, thus forming clinkers; and improper manipulation of dampers. 
It is here that the human equation becomes of most importance. Atten- 
tion concentrated on what takes place from day to day in front of the 
boilers will pay greater returns for the time spent than in any other part 
of the plant. 

In operating a boiler plant observe the following suggestions by the 
Westinghouse Company. 

DON'T FAIL TO: 

1 . Keep the heating surfaces of the boilers free from soot, scale and 
oil. 

2. See that the baffling is in good condition and that the gases follow 
the proper path. 

3. Be sure that the boiler settings are tight and free from air leaks. 

4. Keep the fires level and free from holes. 

5. Use the dampers to regulate the draft. , I 

6. Do not carry the fires so thin or have so much draft as to draw a 
lot of excess air through. 

7. Do not carry the fires so thick or cut down the draft so much as 
to have incomplete combustion of the coal. 

8. Do not soak the coal with water before firing. 

9. Be sure the blowoff valves do not leak. 

10. Do not have the safety valve popping off continually. 

11. Minimize radiation losses by covering steam pipes. 

12. Do not allow the waste of steam through leaky traps, valves, etc. 

13. Never use live steam where exhaust is available and can be used 
as well. 

PROBLEMS 

38. Given the following data from a boiler test: 

1. Kind of boiler, Heine, water-tube. 

2. Kind of fuel, West Virginia, briquettes. 

3. Furnace, hand-fired. 

4. Duration of trial, hours • 10 . 25 

6. Grate surface, square feet 40 . 55 



THE STEAM BOILER 1656 

6. Water heating surface, square feet : ; 2,031 . 

7. Steam pressure, gage, pounds per square inch 83 . 7 

8. Temperature of feed water, °F 52 . 9 

9. Temperature of escaping gases from boiler, °F 590.0 

10. Total weight of coal as fired, pounds 7,515 . 

11. Moisture in coal, per cent 2 . 32 

12. Ash and refuse in dry coal, per cent 10 . 36 

13. Calorific value per pound of dry coal, B.t.u 15,235 . 

14. Calorific value per pound of combustible, B.t.u 16,266.0 

15. Moisture in steam, per cent 0.8 

16. Total weight of water fed to boiler, pounds 62,641 .0 

17. Factor of evaporation 1 . 20 

Find the following: 

1. Ratio of water heating surface to grate surface. 

2. Total weight of dry coal consumed, pounds. 

3. Total ash and refuse, pounds. 

4. Total combustible consumed, pounds. 

5. Dry coal consumed per hour, pounds. 

6. Combustible consumes per hour, pounds. 

7. Dry coal per square foot of grate surface per hour, pounds. 

8. Quality of steam (dry steam = unity). 

9. Water actually evaporated, corrected for quality of steam, pounds. 

10. Water evaporated per hour, corrected for quality of steam, pounds 

11. Equivalent evaporation per hour from and at 212°, pounds. 

12. Equivalent evaporation per hour from and at 212°, per square foot of water 
heating surface, pounds. 

13. Horsepower developed. 

14. Builders' rated horsepower. 

15. Percentage of builders' rated horsepower developed. 

16. Water evaporated under actual conditions per pound of coal as fired. 

17. Equivalent evaporation from and at 212° per pound of coal as fired. 

18. Equivalent evaporation from and at 212° per pound of combustible. 

19. Equivalent evaporation from and at 212° per pound of dry coal. 

20. Efficiency of boiler; heat absorbed by boiler per pound of combustible, divided 
by the heat value of 1 lb. of combustible, per cent. 

21. Efficiency of boiler and grate; heat absorbed by boiler per pound of dry coal, 
divided by heat value of 1 lb. of dry coal, per cent. 

39. Given the following data from a boiler trial : 

1. Heine water-tube boiler. 

2. Iowa coal. 

3. Duration of trial in hours , 9 . 92 

4. Grate surface, square feet 40 . 55 

5. Water heating surface, square feet 2,031.0 

6. Steam pressure, gage, pounds per square inch 82 . 5 

7. Temperature of feed water, °F 48 . 

8. Temperature of flue gases, °F 627 . 

9. Total weight of coal as fired, pounds 10,986 . 

10. Moisture in coal, per cent 14 . 88 

11. Ash and refuse in dry coal, per cent 17 . 4 

12. B.t.u. per pound of dry coal 11,497 . 



165c ENGINEERING OF POWER PLANTS 

13. B.t.u. per pound of combustible 13,385 . 

14. Moisture in steam, per cent . 91 

15. Total weight of water fed to boiler, pounds 55, 180 . 

16. Factor of evaporation 1 . 205 

Determine the values indicated in problem 38. 

40. An office building contains 7,500 sq. ft. of radiation for steam heating, supplied 
from a low-pressure fire-tube boiler of 950 sq. ft. of heating surface. The engine used 
for power purposes, running non-condensing and exhausting into the atmosphere 
consumed in an 8-hr. run 27,700 lb. of steam supplied from a water-tube boiler 
of 950 sq. ft. of heating surface. What boiler horsepower was being developed by- 
each boiler? What per cent, of the manufacturer's rating was developed in each 
case? 

How much coal was probably used in the 8 hr. run for all purposes if the coal con- 
tained 5 per cent, moisture? What was the consumption of the engine per indicated 
horsepower-hour if the switchboard readings were 240 volts and 260 amperes? D.C. 
generator. 

41. What are the approximate boiler efficiencies corresponding to the table of 
equivalent evaporations per pound of dry coal on page 1 77. 

42. Find the (a) factor of evaporation; (6) the equivalent evaporation; (c) the 
B.t.u. output of boiler per hour, and (d) the boiler horsepower required for each of the 
following installations. 

1. A heating system using 2,200 lb. of steam per hour, the steam being delivered 
from the boiler under 5 lb. per square inch gage pressure and at 96 per cent, quality, 
and the- condensate being returned to the boiler at 175°F. 

2. A non-condensing steam engine carrying 150 i.hp.load, requiring with the aux- 
iliaries 29 lb. of steam per indicated horsepower-hour; steam pressure 125 lb. per 
square inch gage; quality 98.9 per cent.; feed-water temperature 110°F. 

3. A 500-kw. steam turbine, requiring with auxiliaries 18 lb. of steam per kilowatt 
hour; steam pressure 160 lb. per square inch gage; superheat 100°F.; feed-water 
temperature 210°F. 

43. Determine the expected equivalent evaporations and boiler and furnace 
efficiencies for 

(a) Class 3 coals, p. 369. 

(b) Class 5 coals, p. 369. 

(c) Class 6 coals, p. 369. 

(d) Florida peat, p. 371. 

(e) Wood, p. 371. 
(/) Coke, p. 373. 

44. A boiler plant consisting of three 250-hp. hand-fired boilers uses No. 3 buck- 
wheat anthracite coal, costing $2.50 per long ton as delivered: Twelve hundred tons 
are used per month at an average equivalent evaporation of 7 lb. per pound of coal as 
fired. The operating labor is in three shifts, each consisting of two firemen and one 
coal passer, paid $2.50 and $2, respectively, per day, 7 days per week. The per 
cent, of ash in the coal by analysis is 14, but the total ash and refuse are approxi- 
mately 19 per cent., costing 40 cts. per ton for removal. 

The use of soft coal and underfeed stokers is considered, the coal costing $3 per 
long ton delivered, the ash content being 8 per cent. An equivalent evaporation of 9 
lb. is anticipated, the labor for operation being reduced to one fireman and one coal 
passer per 8-hr. shift, at the same wage rates. What, if any, will be the reduction in 
cost per 1,000 lb. of steam? On the basis of the same future demand for steam would 
the investment seem advisable? 



THE STEAM BOILER imd 

45. If the above plant were to operate under the same load only 10 hr. per day (one 
shift, $2.50 and $2 per day wage rate), 53^^ days per week, and if it had previously 
been using the $3 soft coal and obtaining an evaporation of 9 lb., would the stoker 
investment still be justified? 

46. Coal of the following analysis is being used in a hand-fired furnace. 

Per cent, 
by weight 

Carbon '. 70.5 

Hydrogen 4.9 

Nitrogen 1.8 

Oxygen 8.2 

Sulphur 0.9 

Ash 13.7 

100.0 
B.t.u. per pound dry 12,750 

Analysis of the flue gas gives the following results: 

Per cent. . 
by volume 

CO2 7.6 

11.9 

CO 0.3 

N 80.2 

Determine : 

(a) The pounds of air theoretically required for perfect combustion per pound of 
coal. 

(6) The pounds of air actually supplied per pound of coal, 
(c) The per cent, excess air. 

47. On the basis of the analyses in problem 46, with a boiler-room temperature of 
70°F. and a flue temperature of 580°F., how many B.t.u. are lost in the dry flue gases 
per pound of dry coal. What per cent, of the heat value of the coal is this heat loss? 

47a. After closing up the leaks in the boiler setting of problems 39 and 40 and 
adopting better methods of firing the following average flue gas analysis is obtained- 

Per cent, 
by volume 

CO2 13.1 

6.5 

CO 0.4 

N 80.0 



100.0 



If in both cases the losses other than the sensible heat in the flue gas are assumed as 
16 per cent, of the heat in the coal, what would be the probable yearly saving in coal 
bill, coal costing $3.50 per ton; the former consumption having been 1,500 tons per 
year. 



CHAPTER VII 
CHIMNEYS AND MECHANICAL DRAFT 

Chimneys. — Chimneys are built primarily for two purposes; first, 
to furnish draft to enable a sufficient quantity of combustible to be burnt, 
and second, to discharge hot or noxious gases at a sufficient height to 
avoid a nuisance. 

Theoretically, the draft power of a chimney depends on the height 
of its top above the grate bars and the respective densities of the hot gases 
and the outside air. 

Let H = height of the chimney above the grate in feet. 
^0 = 493°F. absolute temperature at 32°F. 
h = absolute temperature of outside air. 
^2 = absolute temperature of gases. 
b — theoretical draft power in inches of water. 



5 = 0.01549^ 






This formula is based on the supposition that h is the mean tem- 
perature of the hot gases in the stack. Assuming a mean stack tempera- 
ture of 600°F. with the external air at 62°F. the above formula reduces to 
5 = 0.00736^, on which the following table is based : 



H 


5 


H 


5 


H 


5 


H 


5 


10 


0.074 


60 


0.441 


110 


0.810 


160 


1.178 


20 


0.147 


70 


0.515 


120 


0.883 


170 


1.251 


30 


0.220 


80 


0.589 


130 


0.957 


180 


1.325 


40 


0.294 


90 


0.662 


140 


1.030 


190 


1.398 


50 


0.368 


100 


0,736 


150 


1.104 


200 


1.472 



In practice, chimney height may be determined from the draft re- 
quirements by the following formula: 



H 



0.00736 



= 135.875 



The required draft power depends upon the loss of head due to fric- 
tion in ashpit air admission openings, to friction in passing through 
grate and fuel bed, to losses by leakage of cold air into combustion cham- 
ber, to friction in the boiler passes and finally to flue, economizer and 

166 



CHIMNEYS AND MECHANICAL DRAFT 167 

stack frictions and the difference of temperature necessary to produce 
the flow in the stack. Of these, the loss due to the grate and the fuel bed 
amounts to from 50 to 75 per cent, of the total. The loss from leakage of 
cold air into combustion chamber, from friction in the boiler passes, 
flues, economizer and stacks amounts to from 15 to 35 per cent., leaving 
often as little as 4 per cent, to produce velocity in the chimney gases. 

No satisfactory method has been devised for calculating the necessary 
draft. 

The height may also be determined from the desired fuel consumption 
per square foot of grate per hour. 

Let F = pounds of coal burnt per hour per square foot of grate. 
Then following Thurston: 

For anthracite coal fp _ ■\\2 

8 = 0.001875(7^ - 1)2 and H = ^ ^ S 

For best Penn. or Welsh 

8 = 0.00148F2 and H = ~. 

o 

For Pittsburgh or Illinois ^2 

8 = 0.000833F2 and H = -^^ 

These formulas have only a limited application. 

Natural draft greater than 1.5 in. of water is seldom necessary, and 
higher intensities can much better be obtained by forced or induced draft. 
This limits the height of chimneys to about 200 ft., which is perhaps above 
the economical limit from a cost and construction standpoint. Chemical 
and metallurgical works in the neighborhood of towns require excessively 
high chimneys to remove the noxious gases and a number have been built 
exceeding 400 ft. in height. In many works, however, means have been 
taken to utilize sulphurous, arsenical and other vapors with a large 
measure of success. 

All chimney formulas are based on the hypothesis that the capacity 
or theoretical coal consumption of a chimney varies directly as the area 
(or effective area) and the square root of the height. 

Let C = coal consumption in pounds per hour. 
A = area of chimney in square feet. 
H = height above the grates in feet. 

Then the typical formula may be written thus : 

C = kaVh, 

where K = a, constant. It may be written 

C = K{A - O.eVI) V5 (Kent's formula), 
where {A — O.GVA) is the "effective area." 



168 



ENGINEERING OF POWER PLANTS 



Ei.353''^- 'S'a' i 



%£l.34fii 



£.levation looking East. it^orisperSaFf- Elevation, looking 
'^ \i3igU. 36'8l" .... 

ii4'5)< SCO" 



North. 





Section atEIev43'6* 




EI.B50' 




SectioaatElev.200W 



Section at Elev. I5'0* 



Fig. 115. — Common brick chimney, 96th St. Power House, Metropolitan St. Ry. Co. 

New York. 



CHIMNEYS AND MECHANICAL DRAFT 169 

The value of the constant K^ as given by different authorities, varies 
greatly. Toldt gives K = 5; Prechtl, K = 6.4; Molesworth, K = 9; 
Ser, K = 9.3; Hutton, K = 10 to 16; Seaton and Rounthwaite, K = 12; 
Henthorn, K = 16.6, and Kent, K = 16.65 (using the effective area for 
A); Brinckerhoff (average), K = 18.1. Toldt and Prechtl refer mainly 
to German metallurgical practice, Ser to general French practice, Moles- 
worth and Hutton to English practice, Seaton and Rounthwaite to marine 
practice, Henthorn to American mill practice. 

An average of 30 stacks of various sizes now doing good work gives 
K = 9.4. An average of three notoriously overworked stacks gives 
K = 17.9. 

Ser's figure K = 9.3, was obtained theoretically by allowing for twice 
the amount of air necessary for perfect combustion. By allowing an 
excess of one-half the amount necessary for perfect combustion, which 
result can readily be obtained by the use of automatic stokers, the 
constant K = 12 will be obtained. 

For preliminary calculations the above formula with K = 12, gives 
practical results, but the chimney should be checked by comparison with 
known stacks of similar diameter and height for the final calculations. 

The value of i^ = 12 applies only to brick-lined stacks. In case an 
unlined iron or steel stack is being considered, the value of K may be 
increased to 14 or 15, and for small stacks 16 may be used. 

The base of a brick stack should rarely be less than one-tenth of the 
height. The allowable batter according to different authorities varies 
from 1 in 192 to 1 in 20 on each side, but the best practice lies between 
1 in 30 and 1 in 40 for ordinary brick, with 1 in 60 to 1 in 80 for the 
Custodis or hollow-tile method of construction. 

In brick chimneys practice varies as to the thickness of the walls. 
The linings are not exposed to wind pressure, and consequently can 
be much thinner than the outside wall, but 100 ft. is about the practical 
limit of each step. The usual practice is to make the steps about 50 ft. 
high and 4 in. thick at the top up to a height of 150 ft. 

For higher chimneys the lining should be 8 in. thick at the top. The 
outside walls for chimneys up to 150 ft. high may be 8 in. thick at the 
top, with the steps about 50 ft. high or the upper steps may be as high 
as 60 ft., with 50 ft. for the lower steps. For stacks built on the Custodis 
principle the top courses are from 8 to 13 in. thick, depending on the 
height. The thickness of the moulded brick is increased 2 in. every 
5 meters, or about every 16J^ ft. 

All brick stacks should be topped with a waterproof cap, usually of 
cast iron, although in many cases it is made of stone or monolithic 
concrete. Lightning rods are considered by many engineers as a neces- 
sity, and there is no doubt that many stacks have been saved by their 



170 



ENGINEERING OF POWER PLANTS 




16. — Typical hollow-tile 
chimney. 



Fig. 117.— Steel stack, 
Wilmerding, Pa. 



Fig. 118. — Tapered rein- 
forced-concrete chimney, 
M. W. Kellog Co. 



CHIMNEYS AND MECHANICAL DRAFT 171 

use. If furnished at all, care should be taken that the conductor and 
ground connections are good. 

The best constructions for steel stacks include a number of vertical 
stiffeners riveted to the shell which support horizontal cast-iron or steel 
rings on which the linings are built. The vertical stiffeners are usually 
spaced about 5 ft. apart, and the horizontal rings about 20 ft. apart. 
By this method any section of the lining may be replaced without dis- 
turbing the other sections. The thickness of the metal at the top of the 
stack in such cases is usually % in., increasing J^ in. every 50 ft. Stacks 
in which the linings are not supported may be J4 in. thick at the top, 
increasing J^g in. every 30 ft. 

Guyed stacks of light sheet iron are frequently used for single boilers 
and even for quite large plants especially where the expected life of the 
plant is short. The smaller stacks are made up in lengths of about 20 ft. 
of 3^-in. steel connected by angle rings on the outside or the whole stack 
may be riveted in one piece on the ground and erected with a gin pole. 

For these stacks the value of K in the general formula may be as high 
as 20 as they are usually connected directly to the boiler uptake and are 
exposed to high temperatures. 

Such stacks deteriorate very rapidly and cannot be considered a 
desirable construction, but occasionally circumstances will require their 
use. Galvanized stranded wire cables form the best guys and the 
anchors may be concrete blocks for the larger sizes. For the smaller 
sizes the guys usually lead to the steel building structure. 

During the last 15 years the use of reinforced concrete as a stack 
material has become quite common. These stacks are of many patterns 
and have been quite successful. The later stacks resemble the brick 
stacks on the outside, but cylindrical and bottle shapes are used to some 
extent. 

The advantages claimed for this type of stack are; 

1. Absence of joints, the construction being monolithic. 

2. Rapidity of construction. 

3. Great strength in compression and tension. 

4. Light weight, requiring little foundation. 

Disadvantages. — 

1. Difficulties with forms. 

2. The break at the end of each day's work. 

3. No data concerning life available. 

Many good stacks of this type have been erected in the last few years 
and their cost, appearance and performance compares favorably with the 
other types. 



172 ENGINEERING OF POWER PLANTS 

Evase Stacks. — During the last few years a type of stack has been 
developed in Europe which offers marked advantages both as to cost 
and ease with which the draft may be controlled. The stack action is 
based on the injector principle, but the theory has not been well worked 
out as yet. The stack resembles a Venturi meter set up on end, the 
upper cone or diffuser enclosing an angle of 7°. These stacks are rarely 
over 60 or 70 ft. in height and are usually applied to single boilers or 
batteries, in order that the control may be perfect. It is usually possible 
to attain an evaporation of about 2 lb. of water per square foot of boiler 
surface with the stack alone. For the higher ratings air is injected just 
below the Venturi throat, thereby inducing a higher rate of suction than 
the height of the stack would make. It is possible so to proportion the 
stack and blower capacities that a suction draft of 3 or 4 ins. of water 
may be obtained, but this is usually unnecessary, as drafts of from 1 in. 
to IJ-^ in. will fulfil most of the requirements. 

The following empirical rules may be followed in the tentative design 
of these stacks : 

1. Figure the area and diameter of the base of the stack from the maximum num- 
ber of cubic feet of flue gases per second, using 40 ft. per second as the velocity. 

2. Make the area of the throat 50 per cent, of the stack area. 

3. Figure the height of the suction cone (30° included angle). 

4. The height of the diffuser will be seven times the throat diameter and the 
diameter of the stack at the top of the diffuser will be 1.85 times the throat 
diameter. 

5. The next thing to settle is the size of the air nozzle for inducing draft. This 
is a matter of the static pressure of the available fans and is smaller as this static pres- 
sure is larger. It is usually taken in the neighborhood of 15 in. of water. The 
formula for the diameter ratios then becomes 



r ^ _ / sue 



suction pressure 
motive air pressure' 



Both pressures in inches of water. From this ratio the diameter and area of the 
nozzle may be readily calculated. 

6. The amount of motive fluid must next be calculated, using w = 0.9 area 
■\/2g X 70 X water gage of motive air. Knowing the cubic feet of motive air per 
second and the area of the nozzle, its velocity can readily be calculated, also the veloc- 
ity head, which added to the static head gives the total head furnished by the 
induced-draft fan, whose horsepower can then be calculated by the following formula 

^P- 6,395 X y 

where y is the fan efficiency, usually 0.50. 

hi is the total pressure, inches of water. 

A is area of outlet. 

V is velocity in feet per second. 

These stacks have been used in a large number of the best modern 
stations in Europe, South America and also in the Rand in Africa. 



CHIMNEYS AND MECHANICAL DRAFT 



173 



Flues and Uptakes.— The uptakes on stanclard boilers are usually 
designed for a normal evaporation of SJ^ lb. of water per square foot of 
surface per hour. This, ordinarily with soft coal, corresponds to J^ lb. 
of coal per square foot of heating surface per hour or 133 cu. ft. of flue 
gases per hour per square foot of heating surface. Taking the velocity 




Fig. 119. — Section of boiler house with Evase stacks. 



of the gas at rating to be 10 ft. per second this would correspond to a flue 
area of 0.0037 sq. ft. for every square foot of heating surface. With a 
50 per cent, overload on the boiler this will give sufficiently low velocities 
to make sure that the minimum portion of dust will be carried up the 
stack. Where soft coal is used this area may be safely reduced to 0.003 



174 



ENGINEERING OF POWER PLANTS 



per square foot of heating surface, in fact, on some installations as low a 
value as 0.0025 has been used with success. 

From the beginning of the uptake to the base of the stack the tem- 
perature of the flue gas continually decreases and it is good practice to 
take into account the drop in temperature and also to consider a 25 per 
cent, increase in velocity in the same space. Where increasing again 
in the stack the velocities are approximately: 

Normal Overload 

Velocity at uptake 10 to 15 ft. 15 to 20 ft. 

Velocity at end of jQue. 13 to 18 ft. 18 to 23 ft. 

Main velocity in stack 20 to 30 ft. 25 to 40 ft. 




Fig. 120.— Evase stack. 



These i&gures will be modified more or less due to variable amounts 
of excess air present in the flue gas. 

Flues and uptakes should be as straight as possible and of as large 



CHIMNEYS AND MECHANICAL DRAFT 



175 



an area as is consistent with the general design of the station. Sharp 
right-angled bends should be avoided and if possible the bottoms of the 
flues should be semicircular in section. The main portions of the flue 
for permanent work should be built of steel 34 in., or thicker, the best 
practice being around % in., well stiffened with longitudinal angles at 
corners and cross angles or tees on the outside. No rivets should be 
used in the building up of the flue but square-headed bolts with square- 
headed nuts may be used. Where changes occur, plates should be 
bent wherever possible avoiding sudden contractions and expansions. 




Fig. 121. — Evase stacks at a German plant. 



No paint should be used on the interior of the flue. The best pro- 
tective covering for this purpose is a wash of Portland cement and water 
mixed to a consistency of cold-water paint and applied with a stiff brush. 
The outside of the flue should be covered with 2 in. of asbestos or magnesia 
covering fastened onto wire mesh, which has been wired securely to the 
stiffening angles, the usual construction leaving an inch air space between 
the flue and the covering. 

Suitable expansion joints must be provided if the flue is of any great 
length. 

The methods of hanging the flue deserve careful attention, the best 
way being to support it by steel straps from I-beams properly spaced 
and located just above the top plate of the flue. Suitable clean-out doors 
should be provided and pipes or chutes through which the flue dust 
may be taken away without being scattered over the neighboring 
machinery. 



176 



ENGINEERING OF POWER PLANTS 



Chimney Dimensions. — The following table of chimney dimensions 
may serve as a guide in checking dimensions determined by the given 
formulse. 



Table op Chimney Dimensions 













Height 


, in feet 




Diameter 
















inches 


75 


80 


85 


90 


95 


100 


110 


120 


130 


140 


150 


175 


200 




Commercial horsepower 


24 


75 


78 


81 






















26 


90 


92 


95 


98 




















28 




106 


110 


114 


117 


120 
















30 




122 


127 


130 


133 


137 
















32 






144 


149 


152 


156 


164 














34 






162 


168 


171 


176 


185 














36 








188 


192 


198 


208 


215 












40 










237 


244 


257 


267 


279 










44 










287 


296 


310 


322 


337 










48 










... 


352 


370 


384 


400 


413 








54 












445 


468 


484 


507 


526 








60 














577 


600 


627 


650 


672 






66 














697 


725 


758 


784 


815 






72 
















862 


902 


932 


969 


1,044 




84 
















1,173 


1,229 


1,270 


1,319 


1,422 




96 


















1,584 


1,660 


1,725 


1,859 


1,983 


108 
















2,058 


2,102 


2,181 


2,352 


2,511 


120 


















2,596 


2,693 


2,904 


3,100 



Draft Pressure Required for Combustion of Different Fuels 


Kind of fuel 


Total draft 
in inches 
of water 


Kind of fuel 


Total draft 
in inches 
of water 


Straw 


0.20 
0.30 
0.36 
0.4 
0.5 
0.6 
0.4-0.7 


Slack, very small 


0.7-1.1 


Wood 


Coal dust 


0.8-1.1 






0.9-1.2 


Peat, light 




1.0-1.3 






1.2-1.4 


Sawdust mixed with small coal 

Steam coal, round 


Mixture of breeze and coal dust 

Anthracite slack 


1.2-1.5 
1.3-1.8 









CHIMNEYS AND MECHANICAL DRAFT 
Cost of Guyed Iron Stacks. — 



177 



Approx. hp. 


Height, ft. 


Diam., in. 


Price complete 


25 


40 


16 


$60 




40 


18 


70 




50 


18 


85 


75 


50 


20 


90 




50 


26 


105 




60 


22 


110 


100 


60 


24 


125 




60 


26 


135 




60 


28 


150 


125 


60 


28 


190 




60 


32 


205 


150 


60 


34 


165 


200 


60 


36 


215 


225 


60 


38 


230 


250 


60 


42 


260 


300 


60 


46 


290 


400 


60 


52 


340 




100 


60 


500 



Cost of Brick Chimneys. — 



Approx. 
hp. 



Height, 
ft. 



Diam. 
flue 



Square 



Outside wall 



No. 
brick 



Cost at $14 
per M 



Cost fire- 
brick lining 
H height 



Cost con- 
crete 
fdtn. 



Total 
cost 



85 
135 
200 

300 
400 

750 

1,000 
1,650 
2,500 



80 


25" 


7' 5" 


32,000 


90 


30" 


8' 3" 


40,000 


100 


35" 


9' 10" 


65,000 


110 


43" 


10' 2" 


75,000 


120 


51" 


11' 2" 


87,000 


130 


61" 


12' 6" 


131,000 


140 


74" 


13' 11" 


151,000 


150 


88" 


15' 1" 


200,000 


160 


110" 


17' 10" 


275,000 



$448 
560 
910 

1,050 
1,218 

1,834 

2,114 
2,800 
3,850 



$60 

82 

113 

190 
261 

334 

432 

482 
720 



$90 
144 
198 

252 
306 

360 

414 
468 
525 



$598 

786 

1,226 

1,492 
1,785 

2,528 

3,060 
3,750 
5,095 



The following approximate costs of various sizes of a well-known radial 
brick chimney give an idea of the variation in cost due to increase in 
diameter and height. 



178 



ENGINEERING OF POWER PLANTS 



Size of chimney 


Cost 


Size of chimney- 




Height, 
ft. 


Diameter, 

ft. 


Height, 
ft. 


Diameter, 
ft. 


Cost 


75 
75 
75 
75 

125 
125 
125 
125 
125 

150 
150 
150 
150 
150 


4 
6 

8 
10 

6 

8 

9 

10 

12 

8 
10 
10 
12 
14 


$1,350 
1,950 

2,650 
3.725 

3,500 
4,250 
4,345 
4,675 
5,125 

6,150 
4,350 
7,125 
7,750 

8,275 


175 
175 
175 
175 
181 
200 
200 
200 
200 
200 

250 
250 
250 
250 
250 


8 
10 
12 
14 
21 

6 
10 
11 
12 
14 

10 
12 
14 
16 
16 


$7,050 
7,525 
8,050 
9,725 

11,500 
9,250 

10,500 
7,990 

11,100 

12,500 

16,500 
18,250 
21,500 
20,000 
24,250 



Cost of Special Chimneys. — Christie ("Chimney Design and Theory") 
gives the following cost of chimneys 150 ft. high and 8 ft. internal diameter. 

Approximate cost 

Common red brick $8,500 

Radial brick 6,800 

Steel, self-supporting, full lined 8,300 

Steel, self-supporting, half lined 7,800 

Steel, self-supporting, unlined. 5,820 

Steel, guyed. : . . . . 4,000 



Average Cost of Stacks and Flues. — The average cost of stacks and 
flues (erected) for several installations ranging from 10 hp. to 2,000 hp. 
is reported by one consulting engineer as follows: 

Cost of Stacks and Flues per Engine Horsepower 



Simple non-condensing: 

Engine horsepower . . . 

Cost of stack, per horsepower 
Cost of flues, per horsepower. 

Engine horsepower . 

Cost of stack, per horsepower 
Cost of flues, per horsepower. 

Simple condensing: 

Engine horsepower 

Cost of stack, per horsepower 
Cost of flues, per horsepower. 

Engine horsepower 

Cost of stack, per horsepower, 
Cost of flues, per horsepower. 



10 
$16.00 
2.30 

30 

$8.70 
2.20 



10 
$12.00 
2.30 

40 
$5.70 
2.10 



12 
$14.80 
2.30 

40 
$7.30 
2.15 



12 
$10.70 
2.30 

50 
$5.25 
2.05 



14 
$13.40 
2.30 

50 
$6.30 
2.10 



14 
$9.70 
2.30 

75 
$4.80 
2.05 



15 
$13.00 
2.30 

• 75 
$5.60 
2.00 



15 
$9.40 
2.30 

100 
$4.55 
2.00 



20 
$11.60 
2.25 



20 
$8.50 
2.20 



30 
$6.3G 
2.15 



CHIMNEYS AND MECHANICAL DRAFT 

Cost of Stacks and Fuels per Engine Horsepower. — (Continued) 



179 



Compound condensing: 

Engine horsepower 

Cost of stack, per horsepower. 
Cost of flues, per horsepower. . 



Engine horsepower 

Cost of stack, per horsepower. 
Cost of flues, per horsepower. . 



100 
$4.55 
1.95 

700 
$2.90 
0.90 



200 
$4.00 
1.80 

800 

$2.85 
0.80 



300 
$3.65 
1.60 

900 

$2.80 
0.70 



400 
$3.30 
1.35 

1,000 

$2.75 
0.55 



500 
$3.10 
1.10 

1,500 
$2.70 
0.55 



600 
$2.95 
1.00 

2,000 

$2.70 

0.55 



Forced and Induced Draft. — In the ordinary power plant the chimney 
furnishes the draft necessary to burn the fuel. Systems of forced and 
induced draft have, however, been developed where it has been neces- 
sary to burn more coal, or where because of other difficulties, a better 
command was needed over the draft than could be obtained by a chimney. 
In the forced-draft system the stack is allowed to carry away the products 
of combustion, but the air necessary for the combustion of the fuel is 
forced under the grate by means of some type of blower so located as to 




Fig. 122,— Forced draft. 

deliver into a closed ashpit or into an air-tight fire room. In the induced- 
draft system a much larger fan, working at a lower pressure, is intro- 
duced into the flue, leading from the boilers to the stack, and the draft 
pressure of the stack is augmented by the pressure developed by the 
fan. Of the two systems the forced-draft system is most used, since the 
fan in the induced-draft system is particularly liable to deterioration on 
account of its being exposed to the action of the hot chimney gases. It 
was formerly claimed by the advocates of induced draft that the expense 
of a chimney could be saved by the adoption of this system, and this is 



180 



ENGINEERING OF POWER PLANTS 



true in some few cases. In the large majority of cases, however, the 
plant is so located that a stack of considerably greater height than would 
be considered necessary for draft alone must be provided to carry the 
noxious gases and smoke a sufficient distance above neighboring struc- 
tures. Forced draft came into prominence through the use of the finer 
steam sizes of anthracite for fuel, as it was found that these sizes of 
anthracite could not be burned with any degree of satisfaction with a 
draft above the fire-bed. Some of the more successful of the modern 
types of stokers require forced draft for the burning of bituminous coal, 
and the ease of manipulation of a fire with the combination of forced 




Fig. 123.— Induced draft. 

draft and chimney, has made the use of forced draft quite general. In 
cases where the plant is located at a distance from habitations the induced- 
draft system may be the best to install. 

The best results may be obtained where forced draft is used to force 
the air through the fire-bed keeping a pressure of 0.01 to 0.03 in. of water 
in the furnace above the fuel and allowing the chimney draft to carry 
away the products of combustion. A number of systems using both 
forced- and induced-draft fans connected by automatic devices for 
maintaining such a condition have been devised but the older method 
with hand regulation will usually give better results. 



CHIMNEYS AND MECHANICAL DRAFT 181 

The initial cost of a brick chimney will usually be two or three times 
that of the mechanical-draft apparatus. In small plants, 100 to 150 hp., 
the cost of a guyed steel stack 75 ft. in height, would be considerable less 
than that of a mechanical-draft system, and once erected would cost 
practically nothing for operation. A tall self-supporting chimney for 
larger plants, however, is very costly as compared with a fan system of 
equal capacity. A brick chimney 175 ft. high and 10 ft. in internal dia- 
meter capable of furnishing the necessary draft for a 3,000-hp. plant, will 
cost, including foundation, about $10,000; a duplicate-fan induced-draft 
system about $5,000, a single-fan induced-draft system, $3,500, and a 
forced-draft system, $2,500. 

Duplicate induced draft equipment installed costs approximately 

Boiler hp. Cost 

500 $1,600 

1,000 2,200 

1,500 2,900 

2,000 3,600 

3,000 5,000 

4,000 6,400 

Capacity of Fans and Power Required. — Ordinary fans are built with 
radial blades and are usually sized by the height of the casing in inches : 
thus a 60-in. fan has an impeller of say 42 in. in diameter but the casing 
height is 60 in. They may be built with a single- or double-inlet. 
The usual proportions of the runner and case are determined from the 
"blast area" which is the area through which the fan will discharge 
giving a velocity equal to the peripheral velocity of the impeller. This, 

WD 

for the standard steel-plate fans, is a = — ^ where a = blast area, W = 

o 

width of blades at the tips and D = the diameter of the impeller. W 

is usually about OAD. The radial depth of the blades is usually 0.15 

D. The inlet is then about 0.56D in diameter and the width of the 

casing is the same as the diameter of the inlet. Let Q = cubic feet of 

0.42)2 
air per second and let N = r.p.m. Then a = - — 5 — = O.ISSZ)^ and 

o 

the peripheral velocity = tt -^ = j^ and 0.1331)2 =, ' qj, j)s _ 

144Q 

— ^rp- for dimensions in feet or roughly for Q = cubic feet per minute, 

OAND^ = Q. 

For multivane fans the formula is l.OOiVZ)^ = Q. These deliveries are 
based on certain total pressures (static + velocity) which are dependent 
on the orifice, the peripheral velocity and type of fan and may be shown 
by characteristic curves or taken from the tables. 

When the conditions are known the theoretical horsepower may be 

calculated by hp. = ^ ^ . - , where Q = cubic feet per minute and ht = 
total head in inches of water. 



182 ENGINEERING OF POWER PLANTS 

Steel-plate Fan 
Table of Air Pressures, Capacity and Horsepower 



Water gage, inches 


Capacity, cubic feet per minute per 
square inch of blast area 


Theoretical horsepower to 
move the given volume 


0.2 


12.2 


0.0004 


0.4 


17.2 


0.0011 


0.6 


21.15 


0.0020 


0.8 


25.0 


0.0031 


1.0 


27.3 


0.0043 


1.5 


33.8 


0.0079 


2.0 . 


38.8 


0.0122 


2.5 


43.3 


0.0169 


3.0 


47.5 


0.0224 


3.5 


51.4 


0.0282 


4.0 


54.8 


0.0344 


5.0 


61.2 


0.0481 


6.0 


66.9 


0.0630 



There are many designs of fans on the market which do not agree 
with these formulas and most builders publish tables for distribution 
giving sizes, dimensions and performances of their fans under all ordinary 
conditions. It should be remembered that these published figures refer 
to the delivery and pressure at the fan outlet. Where delivery is through 
ducts, the friction and other lossies of the ducts must be calculated and 
added to the conditions at the fan in order that a proper selection may 
be made. 

Multiblade fans of the Sirrocco and Sturtevant types differ from the 
ordinary fans in having very narrow blades curved forward in the direc- 
tion of rotation. These blades are from 0.05D to O.ID in radial depth 
and are considerably more efficient than the radial-bladed fans for many 
services. 

High-pressure blowers used for cupola blowing and other high-pres- 
sure work have generally cast housings and are made with slightly curved 
vanes. Their efficiency is also high as compared with the steel-plate 
fan. Propeller fans of many types are manufactured ranging from the 
Blackman with very low volumetric efficiency to the Seymour, and 
McEwen type with 30 to 60 per cent, volumetric efficiency. Guided 
propeller fans of the Rateau or Parsons type have higher efficiencies. 

The characteristic curves for steel-plate, multiblade and cupola fans 
for the same diameter of impeller and r.p.m. are given below. 

When a fan has been tested it becomes possible to draw a character- 
istic for that fan which will give a view of its performance over a wide 
range. Such a characteristic is given in Fig. 125. 



CHIMNEYS AND MECHANICAL DRAFT 



183 



Stock fans are usually purchased without guarantee but where good 
results are desired it is better to specify exact conditions and obtain a 























V 




























































^ 


\ 






















cApoia 


BlAwers 








c 


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TP 


A 


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\ 


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r 




























































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An 


tib 


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Fa, 


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^ 










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Q 




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x 




















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:\ 


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y ^ 




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M 


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\ 


/ 










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y 






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10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 SO 70 80 90 100 10 20 30 40 50 60 70 80 90 100 

Ratio of Opening 

Fig. 124. — -Characteristic curves of fans. 



10 



-•>4 



S^ 










\ 


V 


-^^^;p 






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7 




^ 


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tg; 


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I 10000 20000 30000 40000 

Q Cu.Ft.per Minute 

Fig. 125. — Performance curve of Massachusetts fan. 



50000 



guarantee as to delivery and efficiency. In involved cases the fan and 
duct system should be purchased as a unit. 



184 



ENGINEERING OF POWER PLANTS 



Depreciation and Maintenance of Stacks and Mechanical Draft 
Systems. — The depreciation on a well-designed masonry or concrete stack 
is very low. A properly constructed steel stack, lined with brick, 
requires only painting on the outside every 2 years. The depreciation 




Fig. 126. — Steel-plate fan casing, American Blower Co. 
Dimensions of Steel-plate Blowers 



Size 


A 


^ 


c 


D 


E 


p 


G 


H 


■ 


J 


K 


50 


24K 


19K 


22 


29 


3 


20 


21 


16% 


18 


18 


24>^ 


60 


29i.i 


23K 


263^^ 


34 


3 


23 


243^ 


19% 


213-^ 


21>^ 


28 


70 


331.^ 


27 


30H 


40 


3 


26 


28 


23% 
26>^ 


24>^ 


24>^ 


31 


80 


383^ 


31 


34% 


45 


3 


30 


313^ 


27 


27 


35 


90 


42% 


34% 


393^i 


50 


3 


34 


36 


3034 


303-^ 


303^^ 


39 


100 


47M 


38>^ 


.4334 


55 


3 


38 


39 


33 3-^ 


34>^ 


343^^ 


42 


110 


52 


42M 


473^i 
51>^ 


60 


3 


42 


42M 


3734 

4134 


373-^ 


37>^ 


45>^ 


120 


57 


46H 


66 


3 


46 


47 


413-^ 


413-^ 


51>^ 


140 


66 


5434 


60 


76 


3 


53 


53H 


48 


48 


48 


, 58 


160 


75H 


62 


QSH 


86 


3 


60 


603-^ 


54 


54 


54 


65 


180 


84 H 


693-^ 


77 


96 


3 


68 


683-^ 


603^^ 
663-^ 


60 


60 


72 >^ 


200 


93M 


77>^ 


85H 


106 


3 


76 


753-^ 


66 


66 


79>^ 


220 


103 


85 


94 


116 


3 


84 


82 


73 


72 


72 


90 


240 


112K 


92% 
1003-^ 


102>^ 


126 


3 


92 


89 


7934 


78 


78 


97 


260 


1213^ 


111 


136 


4 


100 


96 


85 


84 


84 


104 


280 


130K 


10834 


1193^ 


146 


4 


108 


102 


92 


90 


90 


110 


300 


140 


116 


128 


156 


4 


116 


10934 


98 


96 


96 


117 



Size 


L 


M 


N 


o 


. 


Q 


E 


s 


T 


u 


V 


50 


20 


31 


9 


39 




183^ 


173^ 


12 


4 


15 


9 


60 


23 


35 


9 


43 




21 


20 


14 


4 


15 


9 


70 


27 


38 


9 


46 




233^ 


2234 


16 


4 


15 


9 


80 


293^ 


41 


9 


49 




243-^ 


23% 
253^^ 


18 


4 


15 


9 


90 


33 


45 


9 


53 




263-^ 


20 


4 


15 


9 


100 


363^ 


49 


9 


57 




303^^ 


28% 


22 


6 


15 


9 


110 


40 


52 


9 


60 




32 


3034 

33% 


24 


6 


15 


9 


120 


44 


61 


9 


70 




353^^ 


26 


6 


23 


9 


140 


51 


67 


13 


76 


22 


39 >^ 


37>^ 


30 


8 


23 


13 


160 


57 


73 


13 


82 


22 


43 


4134 


32 


8 


23 


13 


180 


633^ 


80 


13 


89 


22 


46 


4434 


36 


8 


23 


13 


200 


693-^ 


86 


13 


95 


22 


523-^ 


50 


40 


10 


23 


13 


220 


81 


100 


13 


109 


22 


59 


553-^ 


44 


12 


35 


13 


240 


87 


L06 


13 


115 


22 


62 


583^ 


48 


12 


35 


13 


260 


93 


112 


13 


121 


22 


67 


63 3-^ 


52 


14 


35 


13 


280 


100 


118 


13 


127 


22 


70 


6634 


66 


14 


35 


13 


300 


106 


124 


13 


133 


22 


74 


6934 


60 


16 


35 


13 



CHIMNEYS AND MECHANICAL DRAFT 



185 



Speeds, Capacities and Horsepowers of "ABC 
Varying Revolutions 



Steel-plate Fans at 



S^ 


Fan 


5 


60 


70 


80 


90 


100 


110 


120 


140 


160 


180 


200 


220 


240 




Per V. 


785 


942 


1100 


1257 


1414 


1571 


1728 


1885 


2200 


2513 


2837 


3141 


3455 


3769 


100 


Pres. oz. 


.017 


.025 


.034 


.044 


.055 


.068 


.082 


.100 


.134 


.175 


.231 


.273 


.335 


.401 




Cu. ft. 


682 


1121 


1870 


2652 


3840 


5475 


6395 


9565 


14916 


21750 


30221 


41608 


55201 


71941 




Hp. 


.150 


.222 


.370 


.476 


.672 


1.01 


1.37 


2.03 


3.46 


5.47 


7.7 


12.0 


17.1 


25.1 




Per V. 


981 


1178 


1375 


1571 


1768 


1964 


2160 


2356 


2750 


3141 


3533 


3926 


4318 


4711 


125 


Pres. oz. 


.027 


.089 


.053 


.060 


.089 


.108 


.132 


.153 


.212 


.276 


.350 


.435 


.525 


.626 




Cu. ft. 


852 


1402 


2338 


3158 


4809 


6844 


7992 


11945 


18645 


27170 


37767 


52010 


68997 


99910 




Hp. 


.175 


.284 


.439 


.588 


.934 


1.34 


2.06 


2.90 


5.00 


8.15 


12.5 


19.3 


29.2 


43.5 




Per V. 


1177 


1413 


1650 


1886 


2121 


2356 


2592 


2827 


3300 


3770 


4240 


4711 


5182 


5653 


150 


Pres. oz. 


.039 


.056 


.075 


.100 


.130 


.160 


.190 


.230 


.300 


.400 


.503 


.626 


.758 


.904 




Cu. ft. 


1023 


1681 


2805 


3979 


5760 


8110 


9580 


14360 


22374 


32610 


45325 


62412 


82811 


108120 




Hp. 


.200 


.325 


.531 


.756 


1.27 


1.86 


2.74 


3.90 


7.22 


11.3 


19.6 


32.1 


46.2 


68.6 




Per V. 


1374 


1649 


1925 


2200 


2474 


2749 


3024 


3297 


3850 


4380 


4947 


5496 


6046 


6596 




Pres. oz. 


.053 


.076 


.104 


.134 


.172 


.212 


.2o8 


.306 


.420 


.554 


.687 


.848 


1.02 


1.21 


175 


Cu. ft. 


1194 


1962 


3274 


4622 


6729 


9594 


11200 


16715 


26100 


38043 


52883 


72814 


96626 


126089 




Hp. 


.225 


.393 


.647 


1.01 


1.74 


2.46 


3.55 


5.52 


9.91 


17.3 


27.9 


44.2 


67.1 


103.0 




Per V. 


1570 


1884 


2200 


2511 


2828 


3142 


3456 


3770 


4400 


5026 


5654 


6282 


6910 


7538 


200 


Pres. oz. 


.069 


.101 


.134 


.175 


.225 


.274 


.333 


.392 


.537 


.700 


.903 


1.12 


1.34 


1.59 




Cu. ft. 


1364 


2242 


3740 


5304 


7690 


10960 


12830 


19150 


29850 


43520 


60442 


83231 


110422 


143902 




Hp. 


.262 


.478 


.855 


1.26 


2.05 


3.16 


4.69 


7.01 


13.3 


23.7 


39.2 


62.1 


96.8 


154.5 




Per V. 


1766 


2120 


2475 


2829 


3182 


3534 


3888 


4241 


4950 


5654 


6360 


7065 


7774 




225 


Pres. oz. 


.087 


.126 


.172 


.225 


.285 


.351 


.421 


.507 


.690 


.901 


1.14 


1.41 


1.69 






Cu. ft. 


1534 


2523 


4207 


5969 


8655 


12334 


14385 


21500 


33560 


48680 


68000 


93634 


124217 






Hp. 


.300 


.581 


1.03 


1.57 


2.61 


4.09 


5.95 


9.29 


17.0 


31.1 


52.8 


87.9 


142.5 






Per V. 


1963 


2355 


2750 


3143 


3535 


3927 


4320 


4712 


5500 


6283 


7067 


7852 






250 


Pres. oz. 


.109 


.056 


.213 


.280 


.360 


.430 


.520 


.630 


.860 


1.12 


1.48 


1.73 






Cu. ft. 


1706 


2793 


4675 


6332 


9600 


13705 


16000 


23950 


37310 


54200 


75558 


104036 






Hp. 


.375 


.684 


1.22 


1.79 


3.32 


4.97 


7.44 


11.6 


22.5 


41.2 


71.7 


121.4 






Per V. 


2159 


2591 


3025 


3457 


3889 


4319 


4731 


5183 


6050 


6911 


7774 






275 


Pres. oz. 


.131 


.189 


.258 


.337 


.426 


.526 


.623 


.756 


1.04 


1.35 


1.71 








Cu. ft. 


1876 


3083 


5142 


7294 


10578 


15773 


17394 


26278 


41020 


58328 


83104 








Hp. 


.436 


.821 


1.45 


2.35 


3.92 


6.09 


9.09 


14.5 


29.4 


54.7 


89.3 








Per V. 


2355 


2826 


3300 


3771 


4242 


4712 


5184 


5654 


6600 


7539 






300 


Pres. oz. 


.160 


.225 


.302 


.401 


.520 


.630 


.760 


. 910 


1.26 


1.62 










Cu. ft. 


2046 


3363 


5610 


7957 


11520 


16250 


19200 


28800 


44750 


63629 










Hp. 


.500 


.975 


1.73 


2.86 


4.63 


7.44 


11.4 


18.1 


37.5 


69.3 










Per V. 


2747 


3297 


3850 


4399 


4949 


5447 


6048 


6597 


7700 








350 


Pres. oz. 


.216 


.306 


.418 


.550 


.693 


.850 


.970 


1.25 


1.68 










Cu. ft. 


2387 


3923 


6545 


9282 


13410 


19110 


22395 


33400 


52206 








r 


Hp. 


.663 


1.28 


2.38 


3.89 


6.65 


10.7 


17.2 


28.3 


55.8 










Per. V. 


3140 


3768 


4400 


5028 


6656 


6282 


6912 


7540 








400 


Pres. oz. 


.277 


.399 


.546 


.713 


.904 


1.14 


1.42 


1.63 










Cu. ft. 


2729 


4384 


7480 


10620 


15400 


21950 


25574 


38300 










Hp. 


.750 


1.70 


3.19 


5.04 


9.34 


15.3 


25.2 


39.2 









and maintenance charges on a mechanical-draft system will range from 
5 to 15 per cent, of the cost and in the case of induced systems may 
be considerably higher. 

Efficiency With Stacks and Mechanical Draft Systems. — With 
mechanical draft a much thicker fire can- be maintained on the grates, 
thus permitting a high rate of combustion and minimum draft per pound 
of fuel, both of which result in increased boiler efficiency. Where the 
forced-draft system is used a proper manipulation of stack dampers and 
fan speeds leads to a balanced draft from which exceedingly good 
results can be obtained. In this case the chimney has only to furnish 



186 



ENGINEERING OF POWER PLANTS 




Fig. 127.— ^Cast-iron case volume blower. 
Dimensions 



American Blower Co. 



.2 

02 


A 


B 


C 


D 


E 


F 


G 


H 


I 


J 


K 


L 


M 


N 





P 


Q 


R 


S 


1 


7H 


63/^ 


7 


9 


434 


5 


514 


434 


634 


4 


8K 


8K 


3 


2% 


3% 


6 


iHfi 


7 


2 


2 


^yn 


7J^^8 


8K 


io«4 


6H 


6 


6K 


6K 


8K 


5 


11M6 


llMfi 


4 


3 


5% 


634 


134r 


8% 


2% 


a 


l^H 


8K 


9K 


12H 


6^/8 


7 


7K 


7 


934 


534 


1234 


12% 
15% 


5 


3% 


5% 


8 


1%6 


10 


3 


4 


13 y« 


UK 


12^ 


16 


^y^e, 


9 


9y. 


834 


12M6 


7H 


15H 


6 


4 


7 


11% 


1%6 


13 


3% 


5 


16 K 


14^8 


15% 


19 H 


10% 


11 


1134 


1U34 


15^-8 


9 


17 H 


17% 


7 


4% 


8 


13 


1346 


16 


4% 


6 


2Ui/R 


16Vh 


18^6 


23 H 


12 J/^ 


13 


14 


13 


17% 


1034 


20 


20 


8 


5% 


9H 


15% 


1%6 


19 


5% 


7 


23 i^ 


19 a/^ 


21^4 


27 


14K 


15 


16 


15 K 


20% 


12 H 


23% 


23% 


9 


6% 


11% 


18 


1%R 


22 


6 


8 


26 


21K 


24 


30^8 


16H 


17 


18^8 


17K 


23^4 


14K 


26 


26 


10 


7% 


13 


20% 


ly^e, 


25 


634 


9 


29 


24>i 


26% 


34>4 


18% 19 


2034 


19>^2 


26 


16 


29 


29 


11 


8% 


14% 


23 


1^%6 


28 


7% 



Speed, Capacity 


AND Horsepower Required for the "ABC 


' Volume Blowers 




Dia. 
of 


Width 
at 


Cir. 
in 


1% 


z. pressure 


1% 


z. pressure 


2 Oz. pressure 


Size 






















wheel 


per- 
iphery 


feet 


R.p.m. 


Cu. 

ft. 


Hp. 

net 


^R.p.m. 


Cu. 

ft. 


Hp. 

net 


R.p.m. 


Cu. 
ft. 


, Hp. 
net 


1 


8% 


2 


2.22 


3300 


348 


0.350 


3560 


376 


0.445 


3810 


402 


0.545 


2 


10% 


2% 


2.75 


2650 


512 


0.520 


2880 


554 


0.655 


3080 


590 


0.800 


3 


12 


% 


3.15 


2320 


711 


0.728 


2510 


770 


0.918 


2690 


822 


1.17 


4 


15% 


4.06 


1800 


1210 


1.24 


1950 


1305 


1.55 


2080 


1395 


2.53 


5 


19 


5% 


4.98 


1470 


1830 


1.87 


1590 


1980 


2.35 


1700 


2110 


3.83 


6 


22% 


6% 


5.90 


1240 


2600 


2.66 


1340 


2810 


3.33 


1440 


3000 


5.45 


7 


26 


7% 


6.80 


1075 


3420 


3.50 


1160 


3700 


4.37 


1250 


3960 


7.20 


8 


29% 


8% 


7.73 


950 


4130 


4.54 


1025 


4800 


5.68 


1100 


5125 


9.30 


9 


33 


9% 


8.65 


845 


5580 


5.72 


915 


6020 


7.15 


980 


6440 


11.7 





Dia. 

of 


Width 
at 


Cir. 
in 


3 Oz. 


pressure 


4 Oz 


. pressure 


5 O2 


. pressure 


Size 






















wheel 


_ per- 
iphery 


feet 


R.p.m. 


Cu. 

ft. 


Hp. 

net 


R.p.m. 


Cu. 

ft. 


Hp. 

net 


R.p.m. 


Cu. 

ft. 


Hp. 

net 


1 


8% 


2 


2.22 


4670 


492 


1.00 


5400 


568 


1.54 


6100 


635 


2.15 


2 


10% 


2% 


2.75 


3770 


725 


1.47 


4360 


835 


2.26 


4900 


935 


3.17 


3 


12 


3% 


3.15 


3300 


1005 


2.06 


3810 


1160 


3.17 


4300 


1300 


4.44 


4 


15% 


4% 


4.06 


2560 


1705 


3.46 


2960 


1970 


5.35 


3330 


2200 


7.45 


5 


19 


5% 


4.98 


2080 


2590 


5.75 


2410 


2980 


8.07 


2720 


3340 


11.3 


6 


22% 


6% 


5.90 


1760 


3670 


7.45 


2040 


4250 


11.5 


2300 


4750 


16.2 


7 


26 


7% 


6.80 


1530 


4850 


9.85 


1770 


5600 


15.2 


2000 


6250 


21.2 


8 


29% 


8% 


7.73 


1340 


6270 


12.8 


1550 


7250 


19.7 


1750 


8100 


27.4 


9 


33 


9% 


8.65 


1200 


7875 


16.0 


139€ 


9100 


24.7 


1570 


10180 


34.4 



CHIMNEYS AND MECHANICAL DRAFT 



187 



sufficient draft to remove the products of combustion, while the 
forced draft maintains the combustion at the proper rate and produces 
a sHght plenum above the fire, thus preventing the large losses due to 
inrush of cold air when the fire-doors are opened. With mechanical 
draft the amounts of air and pressure can be readily regulated for any 
sudden increase or decrease of the requirements practically independent 
of boiler performance. Damp muggy days appreciably affect the draft 
of the chimney as do adverse air currents dnd high winds^ but these 




Fig. 128. — Niagara conoidal fan. 



Dimensions of Niagara Conoidal Fan 

Overhung Pulley Full Housing — Bottom Horizontal Discharge 

Dimensions in Inches 



Size 


A 


B 


C 


D 


E 


F 


G 


H 


I 


J 


K 


L 


M 


X 


Y 


3 

3H 

4 


12 
14 
16 


15H 
If 


17M 

20 

22% 


11%6 

13 

14% 


15% 

18%6 
21%6 


13% 

15%6 

17% 


20i%6 

24% 

27% 


22 

25% 

29 


16% 
18% 
20% 


11% 

13 

14% 


14 
16 
18 


27% 

i?8 


15 
16 
17 


ill 

3% 


8 

9 

10 


4M 
5 

5H 


18 
20 

22 


23^^ 
26M 
28% 


25% 
28K 
31M 


16% 
18^^ 
20% 6 


23% 


19% 
22% 6 
24% 


31% 

34i%6 

38%6 


32% 

36 

39% 


2;^% 
24% 
26% 


16% 
18% 
20% 6 


20 
22 

24 


11^ 

37 


18 

19% 

19% 


3% 
3% 
3% 


1.1 
li.- 
14 


7 
8 


24 
28 
32 


31H 
36% 
42 


34% 
39% 
45H 


22% 6 

26 

29% 


42« 


26% 
30% 
35% 6 


41% 

48%6 

55% 


43 

50% 

56% 


28% 
32% 
36% 


29% 


26 
30 
34 


66 


22 
29 


4% 
5% 
6% 


16 
18 
20 


9 
10 
11 


36 
40 
44 


47K 
52H 
57M 


51% 
56% 
62H 


33H 

37M6 

4015,16 


58%6 


39% 

44% 
48% 


62% 6 
69% 
76% 6 


64 

70% 
78 


40% 
44% 
49% 


33% 

37%6 

40i%6 


38 
42 
46% 


63% 
67% 
75% 


32 
34 
38 


8% 


24 
26 

28 


12 
13 
14 


48 
52 
56 


63 

683^ 
73>^ 


68 


44% 
48% 
52% 6 


63% 

687:^ 

74% 6 


61% 


83% 
90% 6 

97% 


85 
92 
99 


53% 
58% 
62% 


44% 
48% 
52% 6 


59 


81 

85% 

95% 


41 
43 

48 


10 
11 
13 


30 
34 
36 


15 
16 
17 


60 

64 
68 


78M 

84 

89M 


83% 
90% 
96 


55% 
59% 
63% 


79% 
84% 
90% 6 


66%6 

70% 

75 


104%6 

111 

117i%6 


106 

112% 

119% 


66% 
71% 
76% 


55% 


63 


100% 

109 

115 


50 
54 
56% 


15 


38 
40 

44 


18 
19 
20 


72 
76 
80 


94H 
99% 
105 


lOlH 

107 

112% 


661% 6 
70l%6 
74% 


95% 

1001%6 

106 


IP- 

88% 


124% 

1311%6 

138% 


126% 
133% 
140% 


80% 
84% 
88% 


66i%6 
701% 6 
74% 


76 
80 

84 


122% 

128 

130 


61 
63 
63% 




46 
48 
50 



188 



ENGINEERING OF POV/ER PLANTS 



conditions with mechanical draft will not affect the burning of coal, since 
the amount of chimney draft used is much smaller than the capacity of 
the chimney. 

It is claimed that smokeless combustion is more readily effected with 
artificial draft than with natural draft, as a thicker fire can be carried 
and the correct proportion of air more readily adjusted. 



5 


I& 


^ 






^^■i:w 



Fig. 129. — Runner of conoidal fan, Buffalo Forge Co. 











Capacity Table Buffalo Fans 












Mean 


Area 
of 

out- 
let, 
sq. ft. 


>^" Total press, 
or 0.288 oz. 


1" 


Total press, or 
0.577 oz. 


2" 


Total press, or 
1.154 oz. 


3" Total press, or 
1.734 oz. 


Fan 


dia. of 
blast- 
wheel 














no. 


1 i 




> 


'o 
> 


ft 


> 


i 


ft 


1 


> 


ft 


3 

3H 
4 




1.31 
1.79 
2.33 


478 
409 
358 


1,720 
2,350 
3,070 


0.19 
0.26 
0.34 


675 
579 
506 


2,440 
3,320 
4,340 


0.54 
0.74 
0.97 


955 
818 
716 


3.450 
4,690 
6,130 


1.54 
2.09 
2.73 


1,169 
1,002 

877 


4,220 
5,750 
7,510 


2.83 
3.85 
5.02 


53^ 


IP" 

2SH" 


2.95 
3.64 
4.41 


318 
287 
260 


3,880 
4,790 
5,800 


0.43 
0.53 
0.65 


450 
405 
368 


5,490 
6,770 
8,200 


1.22 
1.51 
1.83 


636 
573 
521 


7,760 

9,580 

11,590 


3.46 
4.27 
5.47 


780 
702 
638 


9,500 
11,730 
14,190 


6.36 

7.84 
9.49 


6 

7 
8 


31K" 
36M" 
42" 


5.25 
7.14 
9.33 


239 
205 
179 


6,900 

9,400 

12,260 


0.77 
1.05 
1.37 


338 
289 
253 


9,750 
13,280 
17,340 


2.17 
2.96 
3.87 


477 
409 
358 


13,790 
18,770 
24,520 


6.15 

8.37 

10.90 


585 
501 
439 


16,890 
23,000 
30,040 


11.30 
15.40 
20.10 


9 
10 
11 


48" 
52" 
57H" 


11.81 
14.58 
17.64 


159 
143 
130 


15,520 
19,160 
23,180 


1.73 
2.14 
2.58 


225 
203 
184 


21,950 
27,090 
32,780 


4.89 
6.04 
7.31 


318 
286 
260 


31,020 
38,310 
43,360 


13.80 
17.10 
20.70 


390 
351 
319 


38,010 
46,930 
56,780 


25.40 
31.40 
38.00 


12 
13 
14 


63" 
68" 
73" 


21.00 
24.65 
28.56 


119 
110 
102 


27,590 
32,370 
37,550 


3.08 
3.61 
4.19 


169 
156 
145 


39,010 
45,780 
53,100 


8.70 
10.20 
11.80 


239 
220 
205 


55,170 
64,730 
75,090 


24.60 
28.90 
33.50 


292 
270 
251 


67,570 
79,300 
91,970 


45.20 
53.00 
61.50 


15 
16 
17 


78K" 
83M" 
89" 


32.81 
37.33 
42.14 


96 
90 

84 


43,100 
49,040 
55,370 


4.80 
5.47 
6.17 


135 
127 
119 


60,960 
69,360 
78,300 


13.60 
15.50 
17.50 


191 
179 
189 


86,200 

98,060 

110,720 


38.40 
43.70 
49.40 


234 
219 
206 


105,580 
120,130 
135,620 


70.60 
80.30 
90.70 


18 
19 
20 


94" 
99" 
105" 


47.25 
52.65 
58.33 


80 
75 

72 


62,060 
69,160 
76,640 


6.92 
7.71 
8.54 


113 
107 
101 


87,780 

97,800 

108,370 


19.60 
21.80 
24.20 


159 
151 
143 


124,110 
138,280 
153,250 


55.30 
61.70 
68.30 


195 
185 
175 


152,020 
169,400 
187,680 


101.70 
113.30 
125.50 



CHIMNEYS AND MECHANICAL DRAFT 189 

The advantages of forced and induced draft may be summed up as 
follows: (1) Draft not limited by atmospheric conditions or height of 
stack; (2) increased capacity of plant, within limits, at will; (3) possibility 
of burning inferior fuel with advantage. 

Disadvantages: (1) High operating cost of the machine; (2) occupies 
space which often is valuable; (3) uses from 1 to 5 per cent, of the steam 
generated by the boiler. 

PROBLEMS 

48. The height of a chimney at the plant of Fall River Iron Co., Boston, is 350 ft.; 
internal diameter, 11 ft. Determine the number of pounds of coal that can be burned 
per hour and the horsepower of the chimney. 

49. The power plant of the Passaic Print Works, Passaic, N. J., has a chimney 9 ft. 
in internal diameter which handles the gases from 13,855 lb. of coal per hour. Deter- 
mine the height of the stack. 

50. The plant of the Amoskeag Mills, Manchester, N. H., has a stack 230 ft. high 
which handles the gases from 19,195 lb. of coal per hour. What is the diameter? 

51. (a) Two boilers in the market have the following heating surface : 

(A) Is a water-tube boiler with 3,350 sq. ft. 

(B) Is a fire-tube boiler with 2,590 sq. ft. 

Under test (A) actually evaporated 144,000 lb. of water in 12 hr., and (B) 108,000 
lb. What was the approximate per cent, of rating carried by each boiler? 

(6) On the basis of the evaporation given in (a), and usual operating conditions, 
how much coal was fired under each boiler per 12 hr. if the coal contained 10 per cent, 
moisture? 

(c) On the basis of (6), what would be the diameter and height of stack required 
for this plant, if one stack serves both boilers? 

(d) With a stack of the dimensions determined in (c), how does its commercial 
horsepower, as given in the table on page 176, compare with that of the given plant? 

52. A plant containing five 300-hp. boilers, four of which are in continuous service 
under approximately 33 per cent, overload, has a chimney 7}^ ft. in internal diameter 
and 160 ft. high. Additional steam demands will require the installation of two 300- 
hp. boilers, these to run at about the same overload. The fuel used is run of mine 
bituminous coal, about 13,000 B.t.u. per pound. Will the present stack be of sufficient 
capacity? 

53. In connection with the above plant, it is finally decided to erect another stack 
to have sufficient capacity to handle three 300-hp. boilers at 50 per cent, overload, 
burning the same grade of coal. The boilers have a ratio of heating surface to grate 
surface of 50 to 1. Estimate the height and the diameter of stack to be used. 

54. Determine a "Handy" (approximate) figure for the required capacity of (1) 
a forced-draft fan in terms of cubic feet per minute per pound of coal burned per hour; 
(2) an induced-draft fan. 

55. It is desired to provide a forced-draft fan of the steel-plate type for a battery of 
boilers of 1,000 hp. rated capacity but from which it is intended to be able to take 100 
per cent, overload. The boilers are to be equipped with underfeed stokers, on which 
the manufacturers guarantee 100 per cent, boiler overload capacity with 3.5 in. of 
water draft. Determine the impeller diameter and width, the r.p.m., and the horse- 
power rating of engine drive required for a steel-plate type of draft fan. 4 



CHAPTER VIII 
SMOKE AND SMOKE PREVENTION 

Smoke is a result of imperfect or improper combustion. The Stand- 
ard Dictionary states that smoke is the volatihzed products of the com- 
bustion of an organic compound, as coal, wood, etc., charged with fine 
particles of carbon. The definition of the word "smoke" given in the 
recent (1915) report on Smoke Abatement and Electrification of Railway 
Terminals in Chicago is "the gaseous and solid products of combustion, 
visible and invisible, including, in the case of certain industrial fires, 
mineral and other substances carried into the atmosphere with the 
products of combustion." 

Smoke consists then of: 

1. Visible properties. 

2. Solid constituents. 

3. Gaseous constituents. 

The ordinary conception of smoke is based upon the effect of particles 
of carbon upon the eye, and the fact is generally lost sight of that, other 
than from an esthetic standpoint, more damage may result from the 
nearly colorless gases issuing from a chimney than from the more offensive 
black smoke. So pronounced is this color impression that the majority 
of ordinances relate specifically to the density of the smoke as determined 
by color charts. The universal standard is a system of charts known as 
the Ringelmann system, which, when placed at the proper distance from 
the observer, give graduations of gray between pure white and black. 
Although the more harmful portions of smoke are practically colorless, 
it is nevertheless true that the color graduation may be an index of 
the efficiency of combustion and may indicate the proportion of inju- 
rious gases that are issuing from a given stack. 

In the ordinary furnace under a steam boiler we find the grate upon 
which the fuel is placed; the openings in the grate through which air is 
supplied ; the combustion chamber in which the oxygen of the air and the 
gases of combustion are thoroughly mixed; and the chimney or stack for 
producing the necessary draft and for carrying away the products of 
combustion. 

190 



SMOKE AND SMOKE PREVENTION 



191 




For perfect combustion there are three primary 
requisites, namely, carbon, oxygen and a chemical 
combination of these elements. In the regular proc- 
esses commercially employed the carbon is secured 
by the use of coal, wood, oil or other fuel; the 
oxygen is secured directly through an ample air 
supply; and the chemical combination of these 
elements is secured by maintaining sufficiently high 
temperatures. 

It is apparent that there are four factors that 
determine to what extent a boiler plant in commercial 
operation will smoke: 

1. The character of the fuel used. 

2. The character of the equipment used for burning 
the fuel. 

3. The care exercised by the fireman. 

4. The state of the atmosphere. 

It is obvious that the problem of smoke preven- 
tion is the problem of perfect combustion. 

Smoke consumption is not possible and there is 
no such thing as a smoke consumer. 

A very common erroneous impression exists re- 
garding the amount of carbon or "good coal" that 
issues from chimneys in the form of smoke. Wild 
statements of enthusiasts on the subject of smoke 
prevention are frequently made to the effect that 
this carbon loss amounts to one-quarter or one- 
third of the fuel charged into the furnace. Such 
statements are absurd, as the amount of 
carbon thus issuing probably seldom exceeds 
cent, at the most. 

Smoke is made up 
of carbon, ash, tar, 
acids, ammonia and 
sometimes small 
amounts of arsenic. 
Recent reports from 
one city in England 
show the relation be- 
tween industrial and 
domestic soot issuing 
from chimneys to be: 



Fig. 130. — Fuel grate, air passage, corobvistiQii chamber and stack of typical plant. 




192 



ENGINEERING OF POV/ER PLANTS 





Industrial plants, 
per cent. 


Domestic plants 




Kitchen, 
per cent. 

■ 


Drawing room, 
per cent. 


Carbon 


27.00 
1.68 
1.14 

61.80 


53.34 

3.68 

12.46 

17.80 


37 22 


Hvdroffen ... . . 


3 51 


Tar 


40.38 


Ash 


4 94 







It is readily seen that the amount of carbon and tar from domestic 
chimneys is relatively far greater than from industrial chimneys. It 
is also correspondingly apparent that the ash from domestic chimneys is 
relatively far less than from industrial chimneys. Domestic chimneys 
are seen, therefore, to have a record that is far from clear and must be 
taken into account in considering the ultimate solution of the smoke 
problem. 

Effects of Smoke. — Briefly, the effects of smoke may be summarized as : 

1. Effect on buildings and building materials. 

2. Effect on vegetation. 

3. Effect on weather conditions. 

4. Effect on health and conduct. 

The smoke nuisance has become such an important factor in connec- 
tion with urban power-plant installations that it deserves the serious 
consideration of all students of engineering. From the exhaustive report 
of the Chicago Association of Commerce relating to Smoke Abatement 
and Electrification of Railway Terminals (1915) the following conclusions 
are taken: 

"A survey of the atmosphere of several of the world's great cities shows an 
improvement in atmospheric conditions during recent years. It shows also that 
Chicago suffers less from the effects of smoke than certain other large cities of 
this and other countries. 

The comparison of the air of cities with that of the country has revealed char- 
acteristics which may and apparently must be attributed to the smoke of the 
cities; but it has also been shown that they may in part be attributed to other 
sources, as, for example, leakage from gas mains, the pollution due to sewers, the 
dust of the streets and decaying organisms. Air analysts have admittedly not 
been able to separate the products of combustion as dispersed in the air from other 
agents of air pollution. 

The industrial activity of all important cities has brought about an increase 
in coal consumption which is greater than the increase in population. Smoke 
formation and the consequent pollution of the atmosphere by smoke have in re- 
cent years tended to increase, and have done so except so far as the adoption of 
various means in smoke prevention have proved effective. The fact is repeatedly 
pointed out that, in securing results of scientific value for use in abating smoke, 



SMOKE AND SMOKE PREVENTION 193 

no one individual and no one city can accomplish the work that must be done. 
The observations must be numerous and must extend over decades. 

The fact appears firmly established that there is a well-defined relation be- 
tween smoke and fog and that the presence of smoke induces fog. It is agreed 
that sunshine is a function of the amount of smoke present in the atmosphere. 

Certain investigations have shown that the amount of carbon dioxide in the 
atmosphere of cities is, as a rule, only about 1 per cent, greater than that in coun- 
try air. The sulphur compounds in the atmosphere are generally due to the 
combustion of coal. 

Among the sources of pollution of city air by smoke, the world over, domestic 
chimneys are conspicuous. The mention of them by observers and students is 
much more frequent than the mention of any other source. 

The most successful means which have been employed to abate smoke have 
included not only legal prohibition but also the development of cooperative and 
educative measures. 

With reference to the effects of smoke, the following conclusions seem 
justified by the literature on the subject: 

(a) There is a general agreement among sanitary authorities that polluted 
air is harmful to health, but at the present time there exists no accurate method 
of measuring this harm nor of determining the relative responsibility of the differ- 
ent elements which enter into the mixture of gases and solids commonly referred 
to as atmospheric air. 

(6) The direct effects of smoke or of any of its attributes, including soot, 
dust and gases, in amounts which may ordinarily pervade the atmosphere of a 
smoky city are not shown to be detrimental to persons in normal health, but the 
general physical tone is lowered as the result of long-continued breathing of pol- 
luted air. 

(c) The direct effect of smoke upon those who are ill has been most extensively 
studied in connection with tuberculosis and pneumonia. It appears that smoke 
does not in any way stimulate the onset of the tubercular process nor militate 
against the rapidity of recovery when once this disease has been contracted, but 
that it has a direct antiseptic effect and tends to localize the disorder. In cases 
of pneumonia, the effect becomes seriously detrimental. 

{d) The tarry matter and sulphur compounds present in coal smoke have 
been shown by experiments to affect certain classes of vegetation when applied 
in sufficient quantities. 

(e) Smoke is popularly regarded as a source of loss and damage in its effects 
upon building materials, objects of virtu, clothing and other property. While 
these effects of smoke seem obvious, it has not been possible to estimate their 
extent with any degree of accuracy." 

''Smokeless combustion of bituminous coal, as defined by present practice 
involves compliance with certain well-defined principles, the more important of 
which may be described as follows: 

1. The fresh coal should be introduced into the furnace at such a point and 
distributed in such manner that the gases distilled from it will be required to pass 
over the incandescent portions of the fire. Observance of this condition exposes 



194 ENGINEERING OF POV/ER PLANTS 

the distillates to high temperatures, aids in their ignition and thereby promotes 
their combustion. The distillates, if not thoroughly burned are prolific sources 
of smoke. 

2. The stream of gases arising from the fresh fuel must be heated as quickly 
as practicable and must be kept at a high temperature until the process of com- 
bustion is well advanced. The presence of a firebrick arch under which the dis- 
tillates may be burned is an. aid in securing this condition. 

3. The interposition of heat absorbing surfaces in close proximity to the fresh 
coal or the burning distillates tends to cool the gases, to suppress combustion and 
to produce smoke. 

4. The admission of air, by which combustion is stimulated, should be pro« 
vided for at proper points and should be subject to careful regulation. 

5. The proportions of the furnace should be such as will provide an ample 
flame way. This condition is necessary in order that the time occupied by the 
gases in passing through the furnace may be sufficient to permit them to burn 
completely. Where the length of the furnace is limited,, the flameway may be 
extended by the use of baffle arches which require the gaseous stream to meander 
through the furnace, producing in effect an elongation of the flameway and pro- 
moting the mixing of the gases. A brick arch in the comparatively small furnace 
of the locomotive serves to increase the length of the flameway, promotes the in- 
termixing of gases and maintains the temperature required for igniting the gases. 

6. Where the dimensions of the furnace are necessarily restricted, and where 
the air admitted cannot be perfectly distributed, the use of small steam jets with 
induced air discharged into the furnace serves to promote the mixture of gases, 
and by so doing, to improve combustion^ The use of such jets with induced air 
on locomotive fireboxes is known to be of material service in suppressing visible 
smoke." 

To obtain entirely satisfactory results from hand-fired furnaces, certain recom- 
mendations for the guidance of firemen are laid down by different authorities. 
Among these are the foUowing: 

1. Fuel should be supplied to the fire periodically in smaU quantities. "A 
furnace well designed and operated wiU burn laany coals without smoke up to a 
certain number of pounds per hour, the rate varying with different coals depend- 
ing on their chemical composition. If more than this amount is burned, the 
efficiency will decrease and smoke will be made owing to the lack of capacity to 
supply air and mix gases." ^ 

2. The accepted methods of supplying coal to hand-fired furnaces are four 
in number, as follows: 

(a) The ''spreading or sprinkling" method; uniform stoking of the entire 
surface of the grate. 

(b) The "coking" method; covering the front part of the grate after pushing 
back the glowing coal. 

(c) The "ribbon" method; partially covering the surface of the grate by stok- 
ing the entire length of the grate and only partially covering the sides, or by stok- 
ing one-half of the grate surface. 

^ United States Geological Survey, Bulletin 373, 1912. 



SMOKE AND SMOKE PREVENTION 195 

(d) The "alternate" method; used when the grate has two or more doors 
through which to feed the fuel." 

"A review of the literature relating to mechanical, physical and chemical 
means of abating smoke shows: 

1. That among the means which have been suggested to reduce the amount 
of smoke in the atmosphere of cities are: 

(a) The removal of fuel consuming industries to points remote from the city. 

(b) The construction of smoke sewers, or community chimneys, of such size 
and height as to permit of directing the discharges from many flues into one 
stack and thereby delivering the combined stream far above the city. 

(c) The establishment of central heating and power plants combining the 
activities of many small coal consuming plants into a few large centers which may 
possibly be located at points removed from areas of congested population. 

{d) The employment of devices for washing smoke discharges before emission 
into the atmosphere. 

(e) The condensation and deposition of smoke particles by means of electric 
devices. 

(/) The abolition of many small coal fires through an extension of the use of 
gas and electricity. 

(g) Improvement in methods of firing. 

2. That fires of bituminous coal may be maintained without becoming sources 
of visible smoke, providing certain principles are recognized in the design of 
furnaces and in the manner in which they are fired. 

3. That it is possible to secure smokeless combustion of fuel fired under sta- 
tionary boilers by hand-firing, though such a result implies careful supervision. 

4. That many types of automatic stokers are available, the operation of which, 
under favorable conditions, is unattended by the production of visible smoke. 

5. That various aids to combustion are recognized which, when applied to 
furnaces, tend to suppress smoke. The more important of these are: 

(a) The brick arch as applied to stationary boilers and as applied to locomo- 
tive boilers. 

(6) The use of bafile walls in furnaces. 

(c) The use of the steam jet with induced air for accelerating the process of 
combustion." 

The complete elimination of smoke in Chicago is set forth by the 
Commission as follows: 

''The complete electrification of Chicago railway terminals would not suffice 
to make the city smokeless. It has been estimated that only from 30 to 50 per 
cent, of all the smoke which pollutes the atmosphere of Chicago comes from loco- 
motives. The remainder is from domestic and industrial fires, small and large. 
Large industrial fires may, through the use of appliances which are well known, 
readily be made smokeless, and it is to fires of this class that the City Smoke 
Department has given most attention. A large percentage of the total smoke 
comes from domestic fires or from industrial fires so small as to make difficult 
the bestowal of sufficient care upon them to secure the prevention of smoke. Any 
plan, therefore, which aims at the development of a smokeless city must deal 



196 ENGINEERING OF POWER PLANTS 

effectively with such small fires. Interpreting this problem, in terms of Chicago's 
fuel resources and our present knowledge of the art, requires a very strict enforce- 
ment of City ordinances not only for the suppression of smoke from equipment 
already installed, but very stringent regulations governing installation of new 
furnace apparatus. With the present administration of the Department of 
Smoke Prevention, under the direction of a competent commission, it is probable 
that a new and better ordinance than that now in force could be of limited value at 
the'present time, but the future will impose requirements not dealt with at present. 
While the policies and methods at present employed in the conduct of the 
Department of Smoke Inspection are, without doubt, correct in a general way, 
there are several matters that should receive particular attention, as follows: 

(a) Much smoke is produced at night, on Sundays and holidays, when the 
city smoke inspectors are not at work. As this smoke is fully as objectionable 
as the smoke made during other times, the immediate establishment of smoke 
inspection service during these periods is recommended. 

(b) When an enlarged organization of the Department has been effected, the 
ordinance should be changed to deal with different grades of smoke instead of 
dense smoke only, as at present. 

(c) The small heating boiler used in apartment houses, small fiat buildings 
and residences is a very crude appliance. The state of the art in its application 
to apparatus of this character is in the same undeveloped stage as that of the 
standard type of boiler furnace years ago and its development has remained 
stationary while that of the power boiler has made great advances. Therefore, 
the development of improved types of low-pressure heating boilers should be 
encouraged and within reasonable time their use made compulsory. 

(d) The use of such smokeless fuels as gas and coke should be encouraged. 
Each is an ideal fuel for domestic and small intermittent fires. The only limita- 
tion to their employment is that of cost and anything that will reduce that cost 
should be encouraged. 

(e) The extension of the plan for supplying steam for heat and power to 
adjacent buildings from a plant centrally or conveniently located with reference 
to those to be served, is a scheme having great possibilities for the elimination 
of smoke, as it makes possible the generation of steam under more favorable 
conditions than prevail in small plants. 

(/) The installation of automatic stokers in the smaller steam-power plants 
should be enforced. 

(g) As there appears to be no way of operating river tug boats without ob- 
jectionable smoke except by the use of anthracite coal, the boats on the Chicago 
River should be required to use such fuel. 

{h) Passenger and freight steamers in the Chicago River should either be 
required to use a better grade of fuel than at present, or mechanical stokers should 
be installed to use the fuel now employed. 

{i) There are many special problems in connection with the prevention of 
smoke that have and will present themselves from time to time, requiring special 
and particular study. Such problems consist in the suppression of smoke from 
furnaces of rolling mills, brickyards, malleable-iron plants, terra-cotta works and 
in similar industries, as well as from automobiles, etc. 



SMOKE AND SMOKE PREVENTION 196a 

COAL BYPRODUCTS AND SMOKE REDUCTION 

"It is not beyond the bounds of reason^ to foresee a condition whereby a house- 
holder, in place of his ton of anthracite which he now welcomes at $11, will receive a 
ton of smokeless coal without slate, a month's supply of cooking gas, 40 miles of motor 
fuel, enough fertilizer to start a small garden and tar sufficient to allay the dust in 
front of his house — all for less money than he now pays for inferior coal." 

1 Gilbert and Pogue, United States National Museum, Bulletin 102, Part 4, 
1918. 



CHAPTER IX 

BOILER AUXILIARIES 

Feed Pumps.- — In the majority of cases an extremely wasteful steam 
engine is used to operate the steam pump for supplying the boiler with 
feed water. As the power required for pumping the feed water is only 
a small portion of the entire amount, an extremely uneconomical pump 
does not represent a great percentage loss of the entire fuel. Further 
than this, as the exhaust steam from the auxiliaries is usually needed for 
heating the feed water the actual steam consumption chargeable to the 
feed pump is not over 10 per cent, of its water rate. 




Fig. 131. — Worthington three-stage centrifugal feed pump with Terry turbine drive. 



Steam Consumption of Feed Pumps. — With compound steam ends 
well lagged and covered 100 lb. of steam per indicated horsepower-hour 
should be safe consumption for feed pumps of large size, while in small 
pumps, 200 lb. appears to be nearer the mark. The pump efficiency 
should not be less than 80 per cent. 

The following illustrates the method of determining the amount of 
steam required by the feed pump to supply a given amount of water 
against a given head. 

Suppose the main engine, radiation and leakage, and all auxiliaries 
with the exception of the feed pump, require 8,000 lb. of steam per hour 
when operating at full rated load, and the boiler pressure is 150 lb. gage. 

1966 



BOILER AUXILIARIES 



197 



The feed pump must now pump not only the 8,000 lb. of water against 
150 lb. pressure, but, in addition, the actual amount of steam required to 
operate the feed pump itself. 

Assuming the economy of the pump to be 200 lb. of steam per indicated 
horsepower-hour and its efficiency to be 80 per cent., and letting "s" 




Fig. 132. — Turbine-driven centrifugal feed "pump, A.E.G., Berlin. 

represent the total steam used by the feed pump per hour, the value of 
*'s" may be found from the following: 

^ (8,000 + g) X 150 X 2.31 X 200 
^ 33,000 X 60 X 0.80 

Centrifugal Feed Pumps. — About 10 years ago it was found to be a 
comparatively easy matter to design a centrifugal pump to deliver water 
at pressures in excess of 200 lb., and the search for an ideal feed pump 
ended in the adoption of centrifugal pumps, using two to five stages, 
driven by steam turbines or electric motors. These pumps were con- 
tinuous in their action, thus putting no severe strains on the feed piping, 
as did the intermittent action of the old duplex or triplex pumps. If the 
feed valves were all shut off by some chance, no accident occurred, since 
the centrifugal pump simply churned the water, but did not deliver it. 
It was found that the pumps were much smaller, required almost no at- 



198 



ENGINEERING OF POWER PLANTS 



tendance and a large saving was made, due to the absence of pump- 
valve renewals, which with hot water, had amounted to a rather large 
figure. ' The steam consumption of the turbines, even when run non- 
condensing, was reasonably low, due to the high rate of rotation, and did 
not increase with age, as in the case of the reciprocating pumps. It was 
no uncommon thing to find the steam consumption of a. 6 by 4 by 6-in. 
duplex feed pump to be 180 lb. per horsepower when new, and this con- 
sumption would increase with the age of the pump until the pump was 
dismantled and the steam valves ground tight. Even when the centrifu- 
gal pump ran at as low a speed as 1,800 r.p.m., the steam consumption 
of. the turbine^, when run non-condensing, would not exceed 50 lb. per 




Fig. 133. — Section of double-suction three-stage centrifugal feed punip. 



horsepower, and this consumption would not increase with age. The 
only defect in the centrifugal feed pump is that 200 gal. per minute is 
about the smallest size which will pay for manufacture, the three common 
sizes being 500, 750 and 1,000 gal. per minute. The price of the cen- 
trifugal feed pump with the turbine drive is about 50 per cent, in excess 
of the reciprocating pump of the same capacity, and the maintenance of 
the pump valves in the reciprocating pump will usually be larger than 
the additional fixed charges. All centrifugal feed pumps should be provided 
with a check valve on the discharge side, with a bypass provided with a 
spring valve between the discharge and suction, for use when all of the 
feed valves happen to be closed, and with a pump governor of some type, 
which will slow down the turbine when much water is not required. 



BOILER AUXILIARIES 199 

Among the special advantages claimed for centrifugal pumps are 

(a) Small floor space. 
(6) Require but little attention. 

(c) Flow of water through the delivery pipe is more uniform than with reciprocat- 
ing pumps; no pulsation or water hammer. 

{d) No serious pressure effects caused by gradual closing of delivery pipe. 
(e) Can be direct connected to prime mover. 

Cost of Feed Pumps. — The cost of feed pumps is a small item in the 
cost of the station, varying from 20 to 50 cts. per kilowatt of station 
capacity, or from 15 cts. to $1 per boiler horsepower the lower prices 



Cost of Feed Pumps (Installed) per Engine Horsepower 



Simple non-condensing: 
Engine horsepower .... 
Cost per horsepower. . . 



Simple condensing: 
Engine horsepower . . 
Cost per horsepower. 

Engine horsepower . , 
Cost per horsepower. 



Compound condensing: 
Engine horsepower . . . . 
Cost per horsepower. . . 



Engine horsepower . . 
Cost per horsepower. 



10 
$5.70 



10 
$5.70 



$3.10 



100 
$0.95 



900 
$0.25 



12 
$5.50 



12 
$5.70 



50 

$2.75 



200 
$0.60 



1,000 

$0.25 



14 
$5.50 



14 
$5.70 



75 

$2.10 



300 
$0.45 



1,500 

$0.25 



15 
$5.40 



15 
$5.70 



100 
$1.70 



400 
$0.40 



2,000 

$0.20 



20 
$4.50 



20 
$5.40 



500 
$0.30 



30 
$3.80 



30 
$3.80 



600 
$0.30 



40 
$3.15 



700 
$0.30 



50 

$2.75 



800 

$0.25 



75 
$2.10 




300 450 600 750 900 
Gallous per Minute 

Fig. 134. — Characteristic curve varying 
conditions, centrifugal pump. 



800 1200 IGOO 

Gallons per M.Lnute 

Fig. 135. — Characteristic curve, 8-in. high- 
speed centrifugal pump. 



200 



ENGINEERING OF POWER PLANTS 



applying to the larger station. Duplex direct-acting pumps, of the 
Worthington type, and suitable for boiler feeding, vary in capacity from 
the 6 by 4 by 6-in., 100-gal. pump to the larger pot-valved pumps with 
compound steam ends 14 and 20 by 10 by 15 in. delivering 500 gal. per 
minute. The price varies from about $300 for the small size to around 
$2,000 for the large size, with the intermediate sizes at proportional prices. 
Centrifugal feed pumps, turbine-driven, run from 200 to 1,000 gal. per 
minute, in about four sizes, and cost about $1,500 in the 200-gal. size and 
about $3,200 in the 1,000-gal. size. Motor-driven centrifugal pumps are 
about 10 per cent, higher in price, and triplex motor-driven pumps often 
run from 100 to 200 per cent, higher. 



GO 120 

110 

50 100 



3 e ™ 

^30S 60 

"S I 50 

^20^ 40 

I (S 30 

?'10 20 



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r.e 


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llOE 


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Fig. 136. — Characteristic curve, variable head and constant-speed centrifugal pump. 



The Injector. — Injectors are sometimes used instead of feed pumps or 
to supplement them. They have to be carefully adjusted for the steam 
pressure used. The temperature of feed water suppHed to the injector 
must be below 150°F. 

Advantages. — 

1. Cheap in small sizes. 

2. Compact. 

3. No moving parts. No cost for repairs. 

4. Delivers water hot to boiler. 

5. No exhaust to care for. 

6. Delivers warmed water without use of feed-water heater. 
These advantages make its use almost universal for locomotives. 

Disadvantages. — 

1. Stops on reduction of steam pressure. 

2. After stopping by failure in steam pressure, often hard to start. 

3. Feed water cannot be much over 100°F. in actual operation. 

4. Is of little use in large sizes. 



BOILER AUXILIARIES 201 

The injector uses about as much steam as the feed pump. The in- 
jector would seldom be used with boilers above 100 hp. except in loco- 
motive practice where its use saves the installation of feed- water heaters. 

Cost of Injectors. — Injector prices average as indicated by the 
formulas in which C = dollars f.o.b. and G = gallons per minute. 

(a) Single tube . . C = 3 + 0.9G 

(h) Double tube C = 5 + LOG 

(c) Restarting C = 10 + LOG 



Feed-water Heaters. — The exhaust from the feed pump and other 
auxiliaries can be largely utilized by the employment of feed-water heat- 
ers, wherein the feed water is heated nearly to the exhaust temperature 
by the exhaust steam. The following claims are made for feed-water 
heaters: for every 11° that the feed water is warmed there is a saving of 
1 per cent, in the fuel burned; with, sufficient exhaust steam available, 
cold feed water may be raised to 205°-210°, saving from 10 to 15 per 
cent, of the fuel. In some localities a heater will pay for itself in a few 
months, depending on the price of fuel. 

Heaters are of two kinds, closed and open. In the closed heater the 
feed water is pumped through copper tubes around which the exhaust 
steam is led. The heat of the exhaust steam is transferred through the 
copper tubes to the feed water and the condensed steam may go either 
to the feed-water tank or to the sump if it is oily. Closed heaters are 
rarely used at the present time, except as primary heaters with bleeder 
turbines or when the exhaust steam is so dirty that the condensate must 
be thrown away. 

Open heaters consist of a chamber in which the exhaust steam and 
feed water are mixed. They usually are of such a size that considerable 
storage is obtained. Where the feed water is very hard they may be 
provided with trays on which the carbonates thrown down by the heat 
are deposited, and frequently they are provided with a sand or excelsior 
filter which catches other impurities. These heaters, when furnished 
with this apparatus, might be termed heater purifiers and are largely used. 
Most of the air contained in the feed water is set free in the open heater 
and escapes through the vent. Various devices are used to deoxygentate 
the feed water. In one the feed water is passed through a tank containing 
iron scrap. In another the feed is boiled by a sudden small drop in 
pressure. Both devices are successful. The closed heater is practically 
a surface condenser working at atmospheric pressure, while the open 
heater is a jet condenser, in some cases with purifying attachments. 



202 



ENGINEERING OF POWER PLANTS 



There is a third type of heater which was introduced a number of 
years ago but has made Httle headway toward common use. A. tray 
or trays are placed in the steam space of the boiler and the feed 
water is delivered into the upper tray, overflowing and being heated by 




100.000 



200,000 300,000 400,000 500,000 600,000 700,000 800,000 900,000 
Capacity in Lbs ./Hour 
Fig. 137. — Characteristic curves of Westinghouse house and fire service pump. 



Steam Outlet 

or Inlet 




Fig. 138. — Closed heater, Berryman type. 

the steam. The impurities collect in the trays, and are removed by what 
corresponds to a surface blowoff pipe. Theoretically there can be no 
saving by the use of a live steam feed water heater. "^Actually the 
reported savings are from 1 to 3 per cent. The most valuable feature of 
this type is the surface blowoff and the assurance that no cold water can 
touch the hot boiler surfaces. See Fig. 140. 



BOILER AUXILIARIES 



203 



Cost of Feed-water Heaters. — The ordinary closed heater has from 
M to 3^^ sq. ft. of heating surface for each boiler horsepower, and costs 
from 75 cts. to $1 per horsepower. 




Fig. 139. — "Cochrane" open heater- 



Approximate cost formulas are: 

For open heaters — 

(a) To 1,000 boiler hp. 

Cost in dollars = 100 + 0.4 X hp. 
(6) 1,000 to 4,000 boiler hp. 

Cost in dollars = 350 + 0.3 X hp. 
For closed heaters — 
To 4,000 boiler hp. 

Cost in dollars = 50 + 0.7 X hp. 



204 



ENGINEERING OF POWER PLANTS 



Cost op Feed-water Heaters Installed per Engine Horsepower 



Simple non-condensing 
Engine horsepower. . . . 
Cost per horsepower. . , 

Simple condensing: 
Engine horsepower. . . , 
Cost per horsepower. . . 

Engine horsepower. . . . 
Cost per horsepower. . 

Compound condensing 
Engine horsepower. . . , 
Cost per horsepower . . 

Engine horsepower . . . , 
Cost per horsepower. . 



10 
$2.95 



10 

$2.95 



40 
$2.15 



100 

$2.85 



900 

$1.00 



12 
$2.75 



12 

$2.75 



50 
$2.10 



200 

$2.55 

1,000 
$1.00 



14 
$2.70 



14 

$2.70 



75 

$2.00 



300 

$2.25 

1,500 
$0.95 



15 

$2.60 



15 
$2.65 



100 
$1.80 



400 
$2.00 



2,000 

$0.95 



20 
$2.50 



20 

$2.50 



500 

$1.75 



30 
$2.20 



30 

$2.30 



600 
$1.40 



40 
$2.15 



700 
$1.10 



50 
$2.05 



800 
$1.10 



75 
$1.90 




Fig. 140. — Double deck boiler with internal feed-water heater. 



Economizers. — Under advantageous conditions, the large waste of 
heat to the chimney may be very largely reduced by the use of a special 
form of feed-water heater of the water-tube type, which may be provided 
with soot cleaners and is located in the flue between the boiler and 
chimney. Such a heater is called an '^economizer." As usually con- 
structed (see Fig. 142) it consists of a bank of cast iron tubes 4 in. in 
internal diameter and 3^^ in. thick. These tubes are about 8 ft. long 
and are arranged with cast iron headers for connection to the feed main. 
The feed water should be heated to about 140°F. before entering the 
economizer. 

Steel tube economizers have been used for many years in marine 
practice but of late years are being installed in connection with sta- 
tionary boilers in certain cases where the station load factor is 50 per cent. 



BOILER AUXILIARIES 



205 



or higher. Such an installation is shown in Fig. 98. In such cases the 
feed water is heated to around 212°F. before entering the economizer 



lOtV f>R£SSU/fB 
CtSTtKON SCONOM/ZE/f 
^RI^CC SSOO Sf. FT 




Fig. 141. 

to prevent internal corrosion. Figure 141 shows a very modern high 
pressure installation with both steel and cast iron tube economizers. 

Economizers are of value in plants operating with steady load in 
which little exhaust steam is available. The annual maintenance usually 



206 



ENGINEERING OF POWER PLANTS 



amounts to 10 per cent, or more of the original cost. Save under excep- 
tional conditions, boiler heating surface is cheaper and usually gives 
better results. 

One writer states that economizers are guaranteed by the manufac- 
turers to save 6.5 per cent, when the temperature of the water entering 
them is as high as 200°F., the economizers having 4.5 sq. ft. of heating 
surface per boiler horsepower and the boilers working at normal rating. 
Several tests show a saving of 10 per cent, with low stack temperatures, 
and an average of 12 per cent, with ordinary stack temperatures. 

The amount saved would ordinarily pay for the cost of the economizers 
in about 3 years. 

They cost about $5.40 per boiler horsepower for plants of 1,000 boiler 
hp. and over on the basis of 4.8 sq. ft. per boiler horsepower; or $6 per 




Fig. 142. — ^Economizer. 

boiler horsepower on the basis of 5 sq. ft. This includes the cost of de- 
Uvering, erecting, brick setting, etc. It is claimed that 3 per cent, of 
the investment will more than pay for the cost of operation, cleaning 
and repairs. 

This same writer gives the following illustrative example: 

1,000-hp. plant. 

Operating 300 10-hr. days per year. 
Coal consumption, Z}4 lb. per boiler horsepower-hour. 
Coal, $3 per ton. 

Annual fuel cost would be $15,750. 
Economizer saving, 12 per cent. = $1,890. 
Cost of economizer, 5.40 per boiler horsepower = $5,400. 
8 per cent, for interest, repairs, operating and cleaning = $432. 
Net saving = $1,458 which is sufficient to pay for the economizer in less than 4 
years. 

If plant were operated continuously, fuel cost = $45,990. 

Net saving = $5,085, sufficient to pay for economizer in about one year. 



BOILER AUXILIARIES 



207 



Potter gives the following cost data for economizers: 

Heating surface per tube = 12-13 sq. ft. 

Lb. water per tube = 60-70. 

Cost f .o.b. factory per tube = $8-$10. 

Cost erected per tube = $12-$15. 

Steel economizers cost about the same as the boilers to which they are attached. 

Barrus reports the following results of economizer tests : 



Heating surface, boiler, square feet 

Heating surface, economizer, square feet 

Temperature of gases leaving boiler, degrees 

Temperature of gases leaving economizer, degrees 

Temperature of feed water entering economizer, degrees 

Temperature of feed water entering boiler, degrees 

Increased evaporation produced by economizer, per cent. 



1,894 


1,058 


5,592 


1,600 


1,920 


1,280 


376 


361 


403 


231 


254 


299 


95 


79 


111 


175 


145 


169 


10.5 


7 


9.3 



3,126 

1,600 

435 

279 

84 
196 

12.8 



and W. R. Roney {Transactions A. S. M. E., vol. 15) reports: 



Plants tested 


1 
610 


2 
505 


3 
550 


4 
522 


5 
505 


6 
465 


7 
490 


8 
495 


q 


Gases entering economizer, degrees 


595 


Gases leaving economizer, degrees 


340 


212 


205 


320 


320 


250 


290 


190 


299 


Water entering economizer, degrees... . 


110 


84 


185 


155 


190 


180 


165 


155 


130 


Water leaving economizer, degrees .... 


287 


276 


305 


300 


300 


295 


280 


320 


311 


Gain in temperature of water, degrees 


117 


192 


120 


145 


110 


115 


115 


165 


181 


Fuel saving, per cent. 


16.7 


17.1 


11.7 


13.8 


10.7 


11.2 


11.0 


15.5 


168 







The N. E. L. A. in the June, 1915 Report of its Committee on Prime 
Movers points out that: 

"Exactly how far to push the question of feed-water heating by economizer 
depends on investment cost, depreciation, operating cost, space required and the 
economy obtained. The increase in economy due to the economizer described 
above amounts to from 10 to 12 per cent. If the feed water were supplied to the 
boiler at the temperature of the steam it would mean an economy of from 16 to 
17 per cent., or a further gain of about 6 per cent. This would reduce the tem- 
perature of the discharge gases to about 200°F. The cost of accomplishing this 
must be more than offset by the gain in economy to warrant such an installation 
— and each case must be considered separately. 

If the temperature of the gas is lowered below the dew point, a deposit of 
moisture occurs on the tubes, with resultant scale and incrustation, and has a 
further objection with western coals, in that the moisture combines with the 
sulphur in the flue gas. forming sulphuric acid. 

The cleaning of economizer tubes of soot does not as yet appear to be satis- 
factorily solved. The scrapers as ordinarily fitted have the effect of rolling the 



208 



ENGINEERING OF POWER PLANTS 



deposit on the tubes, making it difficult to remove. Blowing, both with steam 
and air, has been tried, but generally it has not been successful, or has introduced 
other difficulties which more than offset its usefulness. 

With the present tendency to increase the operating pressure of boilers, it is 
very evident that some change will be necessary in the materials used in econo- 
mizer construction, to assure their adoption, even though the economies obtain- 
able are relatively large. With boilers operating at 225 lb., the feed-line pres- 
sures may exceed 250 ib., and may even at times reach 300 lb., which is generally 
considered too high a pressure to be safely sustained by cast-iron construction. 

The question of steel construction is possibly not entirely settled though the 
cost would be materially increased and there is the liability of excessive corrosion 
due to the chemical properties of certain coals. 



Percentage of Steam Generated Used by Auxiliaries 
(Surface-condensing Plants — Steam-driven Pump) 





Feed 


pump 


Circ 


. pump 


Air 


pump 


"Wh"i 


Steam 

used, 

per 


Kind of plant 
















Econ., 


Eff.. 


Econ., 


Eff., 


Econ., 


Eff., 






lb. 


per cent. 


lb. 


per cent. 


lb. 


per cent. 






75- to 500-kw. horizontal direct- 














500 


12.50 


acting auxiliaries. 


200 


80 


150 


80 


150 


60 


1,000 
1,500 
2,000 
2,500 


15.75 
19.00 
22.00 
24.75 


500- to i ,000-kw. horizontal direct- 














500 


9.00 


acting auxiliaries. 


150 


80 


100 


80 


100 


60 


1,000 
1,500 
2,000 
2,500 


11.50 
13.75 
16.00 
18.25 


100- to 600-kw. engine-driven cen- 














500 


8.75 


trifugal circulating pumps, 














1,000 


11.00 


crank, and flywheel air pumps, 


200 


80 


60 


50 


50 


60 


1,500 


13.00 


direct-acting feed pumps. 














2,000 
2,500 


15.25 
17.25 


600- to 1,000-kw. engine-driven 














500 


7.50 


centrifugal, circulating pumps, 














1,000 


9.50 


crank and flywheel air pumps, 


150 


80 


50 


52 


45 


60 


1,500 


11.50 


derect-acting feed pumps. 














2,000 
2,500 


13.50 
15.50 


Above 1,000-kw. engine-driven 














500 


7.50 


centrifugal circulating pumps, 














1,000 


7.75 


crank and flywheel, air pum.ps, 


100 


80 


40 


55 


40 


60 


1,500 


8.25 


direct-acting feed pumps. 














2,000 
2,500 


10.00 
11.50 



1 " W " is the number of pounds of circulating water per pound of exhaust steam, 
"h" is total head on circulating pump in feet. 



BOILER AUXILIARIES 



209 



Percentage of Steam Generated Used by Auxiliaries 
(Jet-condensing Plants — Steam-driven Pump) 





Feed 


pump 


Circ 


pump 


Air 


pump 


"Wh" 


Steam 

used, 

per 

cent. 


Kind of plant 
















Econ., 


Eff., 


Econ., 


Eff., 


Econ., 


Eff., 






lb. 


per cent. 


lb. 


per cent. 


lb. 


per cent. 






50- to 300-kw. horizontal direct- 














200 


13.00 


acting auxiliaries 


200 


80 


150 


80 


150 


70 


300 

500 

1,000 

1,500 


16.75 
20.75 
25.75 
30.00 


300- to 800-kw. horizontal direct- 














200 


9.00 


acting auxiliaries. 


150 


80 


100 


80 


100 


70 


300 

500 

1,000 

1,500 

200 


11.50 
14.75 
18.50 
25.00 

8.00 


150- to 500-kw. engine-driven cen- 














300 


9.50 


trifugal injection pumps, crank 














500 


11.50 


and flywheel air pumps, direct- 














1,000 


14.75 


acting feed pumps. 


200 


80 


60 


50 


60 


70 


1,500 
200 


19.75 
6.00 


500- to 1,000-kw. engine-driven 














300 


7.50 


centrifugal injection pumps, 














500 


9.25 


crank and flywheel air pumps, 














1,000 


12.00 


direct-acting feed pumps. 


150 


80 


50 


52 


45 


70 


1,500 
200 


16.75 
4.50 


Above 1,000-kw. engine-driven 














300 


5.75 


centrifugal injection pumps. 














500 


7.25 


crank and flywheel air pumps. 


100 


80 


40 


55 


40 


70 


1,000 


9.75 


direct-acting feed pumps. 














1,500 


13.75 



Radiation and Leakage. — In well-designed plants, with properly- 
covered pipe lines, the radiation and leakage losses may be taken as low 
as 3 per cent, of the total evaporation, but usually will run much in excess 
of this figure. 

Oil Pumps. — Small duplex steam pumps are usually used for feeding 
oil to the burners. They are exceedingly uneconomical and a steam 
consumption of over 200 lb. of steam per indicated horsepower-hour 
may be considered a fair average. The efficiency of these pumps is also 
very low, varying between 40 and 50 per cent. It is customary to 
assume the steam consumption of the oil pumps as being 1 per cent. 
of the total evaporation, which is conservative. Centrifugal oil pumps 
have been used to some extent and are much less inefficient and some- 
what higher in cost. 

Oil Burners. — There is a great variety of oil burners on the market, 
some of which have given good satisfaction. They may be divided into 



210 ENGINEERING OF POWER PLANTS 

three classes, depending on the atomizing agent used and the method of 
its mixture with the oil. 

1. Burners using steam for atomizing. 

2. Burners using air for atomizing. 

3. Burners atomizing by mechanical means. 

Practically all commercial oil-burning installations on land use a 
burner of the first type, as it is simpler, more convenient and more eco- 
nomical. These burners may be again divided into those in which the oil 
and atomizing agent are mixed inside the burner, and those in which they 
are not mixed until they leave the burner. Oil-firing does not usually 
meet with the best results, unless large properly shaped combustion spaces 
are provided, and this is best secured with some of the more modern types 
of water-tube boiler. The steam used for atomizing the oil at the burners 
is a direct loss, escaping up the stack as superheated steam. The best 
results show a steam consumption of about K lb- of steam per pound of 
oil, which is something over 2 per cent, of the gross evaporation. In 
ordinary cases the use of atomizing steam amounts to from 3 to 5 per 
cent. Mechanical atomizing burners are largely used in marine work 
and to some extent are appearing in the newer land installations. They 
are much more efficient than the other systems. See paper on Oil Fuel 
by E. H. Peabody, International Engineering Congress, San Francisco, 
1915 (Reprinted by Babcock and Wilcox Co.). 

Boiler Feed Water. — ^Although this is a large subject, the essential 
features, as stated by Shealy in his ''Steam Boilers,"^ are here presented 
in modified form. 

*'The waters of our lakes, rivers, springs, and unaerground streams contain 
more or less mineral substances that have been dissolved by the water in its 
passage through the earth, and also more or less dirt, mud, and vegetable matter 
which have been taken up and carried along by the water. When water is evapo- 
rated in a boiler, all of these impurities are left behind and are usually deposited 
in solid form. In some cases these substances merely settle as a soft mud and 
ean be blown off, but more often they form a hard scale on the heating surface, 
which is difficult to remove. The scale thus formed is a very poor conductor of 
heat and its presence, therefore, reduces the efficiency and capacity of a boiler 
by reducing the amount of heat that can pass through the heating surface. 

It is much better, as far as possible, to prevent the scale-forming substances 
from entering the boiler, as, once inside, they will form a more or less hard scale 
which must be removed. Even though the scale formed is soft and easily re- 
moved, its presence involves a certain expense in laying off the boiler and cleaning 
it. To prevent the formation of scale, requires a knowledge of the chemistry of 

1 "Steam Boilers," E. M. Shealy, McGraw-Hill Book Co. 



BOILER AUXILIARIES 211 

feed water and of the proper treatment by which the mineral salts may be removed 
before feeding the water into the boiler, or they may be changed in nature so 
that they will not form a hard scale but will settle as a soft scale or as mud 
which can be blown o0 or easily removed. 

Impurities in Feed Waters. — The impurities most often found, and found in 
the largest quantities, are given below together with their chemical formulae: 

Calcium carbonate CaCOs 

Magnesium carbonate . ._ MgCOa 

Calcium sulphate CaS04 

Magnesium sulphate MgS04 

The impurities less frequently found and in smaller quantities are : 

Iron carbonate FeaCOs 

Magnesium chloride MgCla 

Calcium chloride CaCLz 

Potassium chloride KCL 

Sodium chloride NaCL 

Besides these there may be iron oxides, calcium phosphate, silica, and organic 
matter, which usually occur in very small quantities. 

The Carbonates. — Calcium carbonate and magnesium carbonate do not dis- 
solve very readily in pure water, but most water contains carbonic acid (CO 2) and 
if this is present, the carbonates dissolve very readily. The carbonates unite with 
the carbonic acid and form the bicarbonates of calcium and magnesium, which are 
very soluble. This combination can, however, be broken up by heating, which 
drives off the carbonic acid gas and returns the carbonates to the insoluble form, 
when they will be deposited. The action described above, begins when the water 
is heated to 180°F. and by the time it has reached 200°F., the greater part of the 
carbonates will be deposited. It requires a temperature of about 290°F. to deposit 
all of the carbonates, but the larger part is deposited between the temperatures of 
180° and 200°F. 

If the feed water enters the boiler at a temperature lower than 180°F. the 
carbonates will be deposited inside the boiler, but, if some device is used whereby 
the feed water is heated to a temperature of about 210° or 212° before it enters the 
boiler, there will be very little of the carbonates deposited in it and it will be 
easily cleaned. 

The Sulphates.— Calcium sulphate and magnesium sulphate are the most 
troublesome impurities as they form an exceedingly hard scale which is difficult 
to remove. The solubility of calcium sulphate in grains per gallon is given in the 
following table. 



Temperature, °F 


Solubility, 


grains per gallon 


212 




125.0 


300 




40.0 


350 




15.5 


400 




12.0 


450 




11.0 


. 500 




10.5 



212 ENGINEERING OF POWER PLANTS 

When other salts are present the solubility is somewhat larger. Live-steam 
feed-water heaters will usually throw down a portion but chemical means must 
be taken to prevent scaling in the boiler as the water becomes concentrated. 

The sulphates possess very active cementing qualities, and not only form a 
very hard scale themselves, but become mixed with mud and other sediment, 
cementing it also into a very dense, hard scale. The best and cheapest chemical 
for this purpose is carbonate of soda, which is also known by the names of soda 
ash, soda crystals, sal soda, washing soda, Scotch soda, concentrated crystal soda, 
crystal carbonate of soda, black ash, and alkali. At temperatures above 200°F., 
carbonate of soda or soda ash acts on the sulphate of calcium and magnesium, and 
also sodium sulphate. The carbonates thus formed become insoluble and deposit 
at this temperature. The sodium sulphate thus formed remains in solution and 
passes into the boiler where it gradually accumulates in the water till it can hold 
no more, when it is deposited. Before it begins to deposit, however, the boiler 
may be blown down and refilled with fresh water. The Hartford Steam Boiler 
Inspection and Insurance Co. states that with an average water, such as that of 
Lake Michigan, requiring 1 lb. of soda ash per 10-hr. day for a 75-hp. horizontal 
return tubular boiler, the boilers should be blown down two gages every 12 hr., 
and should be emptied and refilled with water not less than once in 3 weeks. 

Chlorides. — Magnesium chloride gives trouble because of its cementing 
properties. The other chlorides such as calcium, sodium and potassium give 
little trouble from incrustation unless allowed to concentrate until the water will 
hold no more in solution, when they are deposited and increase the bulk of the 
scale. Magnesium chloride is generally supposed to have a corrosive action on 
the steel plates of the boiler as it reacts with the water, under the influence of 
heat, forming magnesium hydrate and hydrochloric acid, the acid then attacking 
the metal of the shell and tubes. 

Preventing Scale. — The formation of scale and the troubles caused by it have 
already been explained. The feed water should be analyzed and steps taken 
either to prevent the scale-forming elements from entering the boiler or to cause 
their deposit within the boiler in a form that will not adhere to the metal but can 
readily be blown out. If scale has already formed within a boiler, chemicals 
should be introduced to soften it and it should then be removed by washing, if 
softened sufficiently, or if not, by mechanical means. If the scale is very 
hard and flinty, it indicates that there is a considerable percentage of the sul- 
phates present. The carbonates form a very soft scale. 

Foaming and Priming. — A boiler is said to foam if the steam space is partially 
filled with unbroken bubbles of steam, and to prime if the steam carries water 
with it from the boiler. 

Foaming is caused by any materials, either dissolved in the water or suspended 
in it, which retard or interfere with the free escape of steam from the water in the 
boiler. A collection of scum on the surface of the water is also a common cause of 
foaming. Scum may be caused by oil, vegetable matter, or sewage which collects 
on the surface of the water, forming a coating which is hard for the steam bubbles 
to break when they rise to the surface If the water contains an alkali, and any 
animal or vegetable oil becomes mixed with it, the alkali wiU chamge the oil into 
soap, which forms suds and causes foaming. In many power plants the exhaust 



BOILER AUXILIARIES 213 

from engines or pumps is condensed, collected into hotwells, and fed back into the 
boilers. If the cylinders are lubricated with animal or vegetable oil, there is dan- 
ger of its getting into the boiler and causing foaming. For this reason, only a 
mineral oil should be used in the cylinder but, even with this, great care should be 
taken to prevent its entering the boiler, as it is a frequent cause of burned plates. 
Oil extractors placed in the exhaust pipe will aid in removing oil. Open feed- 
water heaters are usually provided with oil extractors, and feed water taken from 
such heaters is almost entirely free from oil. 

Foaming may also be caused by the concentration of certain salts in the water. 

Priming is, in general, caused by the following conditions, all of which should 
be looked after: 

1. Failure to blow down regularly and sufficiently (chief cause). 

2. Failure to clean the boilers regularly. 

3. Presence of oil, alkalies or vegetable matter. 

4. Type of boiler. 

Corrosion. — Corrosion is most often caused by the presence of a free acid in 
the feed water. The free acid may result from the supply of water being con- 
taminated, from adulterants in the cylinder oil which find their way into the boiler, 
or from the splitting up of certain salts in the water. 

All water contains more or less air, which is liberated when the water is heated 
and which attacks metal surfaces. Air absorbed in water is more active in at- 
tacking metal than free air. This is probably due to the fact that more oxygen 
than nitrogen is absorbed by the water. 

The ordinary ingredients of scale, carbonate and sulphate of lime, have little 
or no direct corrosive action unless the scale becomes too thick and causes over- 
heating. In fact a slight coating of these salts acts as a protection and, in some 
cases, when the water fed into the boiler is exceptionally pure, the interior of the 
boiler may be lime washed at cleaning time with advantage. , 

Another frequent cause of pitting and corrosion is a galvanic action which 
goes on in some boilers^ particularly in marine practice. This may be stopped by 
placing pieces of zinc in various parts of the boiler. The zinc will be eaten in- 
stead of the steel and, therefore, will need replacing frequently. 

Treatment of Feed Water.— In case the feed water is known to contain 
impurities, a sample of it should be submitted to a chemist who makes a specialty 
of analyzing feed water, for analysis and prescription for the remedy of be applied. 
This course should also be followed in the case of a new plant. When the location 
for a new plant is to be chosen, particular care should be taken to secure a suffi- 
cient supply of good water. 

The term ''good" as applied to feed water is only relative, but the following 
designations are generally used, based on the number of grains of scale-forming 
substance in each gallon of the feed water: 

Less than 8 gr. per gallon Very good. 

From 8 to 12 gr. per gallon Good. 

From 12 to 15 gr. per gallon Fair. 

From 15 to 20 gr. per gallon Poor. 

From 20 to 30 gr. per gallon Bad. 

More than 30 gr. per gallon Very bad. 



214 



ENGINEERING OF POWER PLANTS 



Water containing as much as 20 to 30 gr. of scale-forming materials to the 
gallon should never be used unless the water is first purified. 

For convenience of reference, the different impurities to be found in feed 
water and the remedies to be applied are collected in the following table : 



Troublesome substance 


Trouble 


Remedy 




Incrustation 
Incrustation 
Incrustation 
Incrustation 

Incrustation 
and corrosion 
Priming 
Corrosion 
Corrosion 

Foaming 

Priming 

Corrosion 


Filtration, blowing off. 


Readily soluble salts 


Blowing off. 


Bicarbonates of lime, magnesium and iron 
Sulphate of lime 


Heating feed. Addition of caustic lime. 
Addition of carbonate of soda or barium 


Chloride and sulphate of magnesium 

Carbonate of soda in large quantities 

Acid 


chloride. 
Addition of carbonate of soda. 

Addition of barium chloride. 
Alkali. 


Dissolved carbonic acid and oxygen 

Grease (from condensed water) 


Heating feed water. Addition of slacked 

lime. 
Slacked lime and filtering. Carbonate of 

soda. Substitute mineral oil. 
Precipitate with alum, or ferric chloride and 


Organic matter (sewage) 




filter. 




filter. 



The Permutit water purification process which has been recently 
introduced depends, for its action, upon the power of "base exchange" 
possessed by zeolites. The process consists of pumping the raw feed 
water through a tank containing an artificial zeolite made by fusing kao- 
lin, feldspar, pearlash and soda. This material is broken up into small 
pieces and packed in the shell. The calcium and magnesium compounds 
are converted into sodium compounds which are very soluble. When the 
Permutit becomes exhausted, it is regenerated by a strong solution of 
common salt which is allowed to remain in contact with it for about 8 hr. 
This process is not practical with a large amount of lime salts in solution 
as the cost is prohibitive. Cold processes for water softening are quite 
largely used and with bad waters are beneficial but are somewhat costly 
The cost of treating may vary from 3^ ct. per 1,000 gal. to as high as 7 
or 8 cts. per 1,000 gal. Where the Permutit process may be used its 
cost should not exceed 4 cts. per 1,000 gal. Hot processes are best worked 
in the open feed-water heater which should be provided with large water- 
storage capacity and filtering arrangements. 

Soot Blowers. — In modern installations of both water- and fire-tube 
boilers, soot blowers are regularly installed as a part of the permanent 
equipment and are used as often as maybe necessary to secure good opera- 
tion. These tube cleaners consist of a set of nozzles so set that all the 
tubes of a fire-tube boiler can be cleaned at once. In water-tube boilers 
a set of nozzles are provided for each pass and the nozzles are so arranged 



BOILER AUXILIARIES 



214a 



that practically the whole heating surface may be covered. Steam 
or air is used and the tubes are cleaned while the boiler is in light service. 
The installation cost varies from 50 cts. to $2.50 per boiler horsepower. 




Fig. 143. — ^Vulcan soot blowers applied to Babcock & Wilcox boiler. 



PROBLEMS 

56. The owner of a maufacturing plant is about to install a 400-hp. compound con- 
densing Corliss engine with surface condenser, water-tube boilers and the necessary 
auxiliaries. The cooling tower will be placed on the roof of the building, 70 ft. above 
the pump pit. 

1. How much steam ought the boilers to supply per hour when the engine is oper- 
ating at full rated load? 

2. He proposes to install three boilers of equal size, two of which shall supply the 
steam demand in (1) when operating at 25 per cent, above the manufacturer's rating. 
How many square feet of heating surface should each boiler contain? 

57. Determine the amount of steam used by a feed pump per hour for each plant 
indicated in problem 18, page 81. 



2146 



ENGINEERING OF POWER PLANTS 



58. A 500 kw. unit with compound condensing high speed engine with auxiharies 
has been installed. The coal used in the plant is Pennsylvania bituminous coal, 
13,500 B.t.u. per lb, dry, 6.5 per cent, moisture. 

What will be (a) the probable total plant consumption per hour and (6) the con- 
sumption per kw.-hr. of coal as fired when the percentage of rated load on the gen- 
erator is 



A 
100 



B 
75 



C 
40 



D 

20 



59. The load curve for a factory unit consisting of 225 kw. D.C. generator direct 
connected to a compound condensing, low speed reciprocating steam engine is as 
shown below. 



240 Kw. 
200 Kw. 
ICO Kw. 
120 Kw. 

80 Kw. 

40 Kw. 













-^ 






















/ 








^ — 
















/ 






Z'' 




\, 










^.^^ 














s 


V 
























s 






1 


















^ 
























































































u 


































k 


^ 






















X 



6 A.M. \ 8 9 10 U 12 1 P.M. 2 

Problem 59. 



5 6 P.M, 



Determine the total quantity of dry steam for each hour from 6 A. M. to 6 P. M. 
which the boilers must supply. 

Note. — It will not be necessary to work more closely than the average load for 
each hour. 

60. The load curve for a factory unit consisting of a 500 kw. D.C. generator, 
direct connected to a condensing Westinghouse- Parsons steam turbine is as shown 
below. 

coo Kw. 
500 Kw. 
400 Kw. 
300 Kw. 
200 Kw. 
103 Kw. 

6 A.M. 7 8 9 10 U 12 1 P.M. 2 3 4 5 6 P.M. 

Problem 60. 













^^•^ 






















/• 






















7 






/ 




\ 
























\ 










/^^ 
















^, 






f 


















> 






1 
























1 




















I 




1 
























1 










LJ 










I 




1 




















\ 


/ 






















-L 



Determine the total quantity of steam (150°F. superheat) for each hour from 
6 A. M. to 6 P. M. which the boilers must supply. 

Note. — It will not be necessary to work more closely than the average load for 
each hour. 



CHAPTER X 
PIPING 

Although the choice and arrangement of certain generators and prime 
movers determine in a general way the efficiency under which a generating 
station can work, yet the piping systems may influence this result to a 
much greater extent than is generally believed. 

The size and arrangement of the various pipes and valves have a very 
important influence on the efficient and economical operation of the 
plant. The piping system may be classified under the following heads: 

High-pressure steam piping, main and auxiliary. 

High-pressure drip piping and boiler returns. 

The feed- water piping (high pressure). 

The exhaust piping. 

The circulating water piping for condensation. 

The hot well and low-pressure drip piping. 

The make-up feed piping and city water supply. 

The jacket and wetting-down piping. 

Compressed-air piping. 

Oil piping, both low-pressure for lubrication and high-pressure for 
step bearings, and 

The fire lines, which are ordinarily considered part of the plumbing 
contract and put in separately from the pipe job. 

In the design of these various systems consideration must be given 
to drainage and returns (traps and steam loops), expansion bends, slip 
joints, etc., vibration, angles and supports, and the various materials 
which are proper to use for the different purposes which the piping sys- 
tems must fulffil. The joints or flanges, the gaskets to be used between 
the flanges, the design of the fittings, elbows, tees, etc., the types and 
designs of the valves, must all be considered in connection with each 
class of piping. 

Pipe. — The material for steam pipe, whether high or low pressure, is 
now almost uniformly openhearth steel. This may be made by the acid 
or basic process, but Bessemer pipe or wrought-iron pipe should not 
be used if the best results are to be obtained. The use of Bessemer-steel 
pipe brings in difficulty in flanging and bending is usually uncertain at 
the welds. It has in its composition rather more phosphorus and sulphur 
than is considered good when severe strains are to be placed on the mate- 

215 



216 ENGINEERING OF POWER PLANTS 

rial. Wrought-iron pipe, when it can be obtained, may be very good for 
certain uses but it is almost impossible to flange a piece of wrought-iron 
pipe satisfactorily and its use is now confined mainly to small sizes for 
steam and hot water. Special dies should be used in threading this pipe. 
Steel pipe when used for oil or salt water is often galvanized and its 
thickness should be proportioned to meet the pressures in use. Where 
warm water is to be distributed, cast-iron pipe has been and is the stand- 
ard but wrought iron pipe is largely used. Cast-iron pipe, when properly 
made, has proved to be the best for large and small water mains for 
either low or high pressures. Where the water pipe is small or where 
many bends "are required, or where the heat and wear are excessive, 
brass pipe has been substituted for cast-iron with very good results. 
The smaller sizes of pipe used in the oiling system are almost invariably 
made of brass. The use of copper pipe for steam work has been almost 
entirely superseded, the introduction of superheated steam with the 
resulting action of the high temperature on the copper rendering it unfit 
for such employment. There are many stations in which nothing but 
openhearth steel and cast-iron piping are used and it may be noted 
that this practice is increasing and these materials will be the standard 
for the future. 

Joints. — Pipe joints have been a great source of trouble in the past 
and the various kinds and ^^ standards" have been as many almost as 
there were individual engineers. . For low-pressure pipe work the screwed 
joint with the standard pipe thread and cast-iron flanges has been and is 
the standard for the best work. For press-ures above 100 lb., however, 
another type of joint should be adopted if the best work is desired. For 
this purpose there has been no joint found better than the so-called Van 
Stone joint. This is made by flanging the end of the pipe against the 
outside of a steel or cast-iron flange. There are many varieties of welded 
flanges in which the flange is welded directly to the pipe, but these do 
not seem to have been as popular or as good in construction as the so- 
called Van Stone, although many people use them. All welded flanges 
have the disadvantage that they cannot be turned on the pipe, making 
great care necessary to avoid mistakes in drilling them. 

The best joints are made by grinding the seats to a perfect surface 
and then bolting them together without a gasket. This, however, takes 
a high grade of mechanic and has been satisfactory only when made in 
the proper manner. Instead of grinding the faces, it is now considered 
at least as good to fine tool finish them and insert an asbestos gasket. 
Duralite and other indurated fibers make good gaskets. Copper gaskets 
appear to deteriorate very rapidly in this position and are not used on 
high-pressure work as much as formerly. The tongue and groove joint 
cannot be recommended for steam work as it is almost impossible to 



PIPING 217 

bring two joints to the same degree of tightness. For the lower steam 
pressures copper gaskets work very nicely and are now standard. These 
are usually stamped with corrugations which flatten out when the bolts 
are tightened up, assuring a surface practically the whole width of the 
face. For exhaust work rubber with wire insertion such as the '^ Rain- 
bow" is mostly used. For water, whether hot or cold, the '^Common 
Sense" or other babbit composition gaskets are quite satisfactory The 
gasket made up of a soft lead ring with a copper wire ring outside of it 
has also been largely used with very good results and ^'Rainbow" gaskets 
are satisfactory when the pressures are not too high. 

Fittings. — For low-pressure work, either steam, exhaust or water, the 
American Society of Mechanical Engineers has adopted a standard of 
pipe fitting which is practically used throughout the United States and 
it is only for pressures higher than 300 lb. that special fittings are required. 
Up to 200 lb. steam pressure with no superheat, cast iron or gun iron 
forms the ideal material for pipe fittings and is practically the only 
material in use. With the advent of superheated steam, however, the 
cast-iron fittings soon proved themselves to be useless with the high 
heats and semi-steel and steel fittings were tried with the best of results. 
Today no plant using superheated steam installs cast-iron fittings for 
high-temperature work. All fittings should be provided with proper 
means of draining and drainage pockets or outlets should be placed at 
the lowest points for the attachment of the drainage system. 

Valves. — For low-pressure work the standard cast-iron valves with 
bronze seats have been more than satisfactory. They are now made of 
a great many types, all of which give very good results. The solid wedge 
gate is perhaps the earliest and the best known. The split-wedge type 
and the parallel two-gate type are also well known and largely sold. 
Globe vales are not usually used for steam work on account of the resist- 
ance offered to the passage of the steam, but for the throttle valves and for 
stop valves are still the standard. For high-pressure work and especially 
with superheated steam the use of the steel-body valve with Monel seats 
and discs has become standard and many varieties of valves are now on 
the market, some of which are doing excellent work. Nickel-bronze and 
nickel are also used for seats and stems with good results. In choosing 
a valve for high-pressure and high-temperature work, great stress should 
be laid on the absence of chance for unequal expansion in the body and 
gates. The metal should be so placed that what expansion occurs will 
be equable in all directions and the gates so designed that they cannot 
spring out of true under different degrees of heat. Such mechanism as 
may be used between the gates in a double-gate valve to press them up 
against the seats should be as carefully designed as the body of the valve, 
as small deflections in this part of the mechanism will prevent tightness. 



218 ENGINEERING OF POWER PLANTS 

The most satisfactory valves for this work have been of the single-wedge 
type, although there are good parallel seat and double-wedge valves on 
the market which have stood severe tests. 

Bolts. — It has been customary in ordinary work to use the standard 
sizes of bolts as provided by the A.S.M.E., using a number of bolts of 
reasonably small diameter. These bolts are the ordinary iron or Bess- 
emer-steel stock with square heads and semi-finished hexagonal nuts. 
If these bolts are made of good openhearth steel and are set up in the 
proper manner, it is an insurance against troubles in the pipe joints 
whereas the ordinary bolt will probably stretch enough to cause more or 
less trouble, not to say anything of the action of the hot steam upon the 
bolts. A leaky pipe is more than a nuisance, for when it has persisted 
for some time it means that the flanges must be refinished before a tight 
joint can be obtained. 

High-presstire Steam Piping, Main and Auxiliary. — The high-pressure 
steam piping of a power station consists first of a steam line taking the 
steam from the boiler drums and delivering it into, second, the first steam 
main or steam header, and third, the connections from the steam header 
to the various prime movers. The auxiliary steam may be taken from 
the boiler drums into the auxiliary header with connections to the aux- 
iliaries, or the connections to the auxiliaries may be made from the main 
itself, or from the connections to the prime movers. All of these systems 
are in satisfactory use. 

The type of the main steam lines, however, depends very largely upon 
the layout of the station. With the end-to-end layout, in which the 
boilers are placed at one end of the station and the prime movers at the 
other end with main steam line connecting the two, the piping may be 
likened to a tree, the boiler piping being the roots, the trunk of the tree 
the steam main and the branches of the tree the feeders of the prime 
movers. 

This type of station is very rarely built at the present day on account 
of the sizes necessary for the steam main through which all of the steam 
must pass. For stations larger than about 5,000 kw. it is never used and 
the ordinary arrangement is the back-to-back where the boilers are ar- 
ranged in one line and the prime movers in another parallel line, with the 
steam line parallel to both and between them. The boiler connections 
then are taken directly to the main and the leads of the prime movers 
directly from the mains to the prime movers. This system is modified 
into a unit system by leaving out the steam main and by introducing 
small equalizing pipes between the unit lines connecting a group of boilers 
with the prime movers. Further modifications of this layout were 
brought out by the use of the double-decked station in which the prime 
movers are placed in the basement with the boilers overhead or the boilers 



PIPING 219 

are placed in the basement with prime movers overhead. Stations of 
both of these types have been in operation for a long time. There are 
also stations with the prime movers in the center and a double line of 
boilers on either side of the engine room. This brings in complications 
in the steam piping, but is frequently economical in cost. 

Disadvantages of Various Systems. — The first system described, or 
the trunk system, is quite a costly system to install and as all of the 
steam had to pass through one section of the main it necessitates very 
large pipes and the consequent serious increase in the cost; the expansion 
difficulties are magnified by the length of the main steam line and except 
for very small plants it is no longer used. 

The parallel system is probably the most used of all systems and the 
unit system and ring-header system are modifications of it. In the ring- 
header system the steam main is a continuous ring which may extend 
around the prime movers, or may be simply a loop between the prime 
movers. The unit system is frequently turned into a ring-header system 
with smaller pipe connections between the parts of the unit system. 
Figs. 144, 162, and 168, show various steam-pipe layouts of these types. 

The unit system almost invariably presents the cheapest and most 
satisfactory system of piping, the steam lines being smaller in size. 
It suffers the disadvantage that when the prime mover is out of service 
the boilers connected to it are also out of service. The parallel system is 
probably more popular than the unit system and is very frequently used. 
The cost of this stands next to the unit system and is about the same as 
the unit system with the cross-ties, which, in reality, convert the unit 
system into a parallel system. The ring-header system is probably the 
most used and is without doubt the most flexible, but is also much more 
costly to install on account of the double line of main headers which are 
usually the largest steam pipes in the station. 

There is a great difference of opinion among engineers as to the best 
method to be followed in these layouts. Formerly it was considered 
necessary to install a duplicate system of steam mains, each boiler having 
a connection to each of the two mains and each prime mover con- 
nections to both mains also. This led to a complete duplicate set of 
steam piping which was extremely costly and usually gave a great deal 
of trouble. It is very easy to keep a steam line tight when it is hot all 
the time, but a steam line first hot and then cold is usually much more 
troublesome. In cases where the duplicate system was installed, one 
of the lines has been removed and the stations are now running on a 
single system with much better results. The losses in a steam piping 
system are entirely due to radiation, the drop in steam pressure due to the 
friction in the pipe being manifested in heat and radiated from the surface 
of the pipe. It is now considered the best practice to make these pipes 



220 



ENGINEERING OF POWER PLANTS 




ft 



PtPtNG 221 

as small as possible allowing at least from 3 to 5 per cent, drop between 
the boiler drum and the prime mover. By cutting down the size of the 
pipe the surface is reduced and as the radiation is directly proportionate, 
to the surface large savings are made. 

Formerly steam mains of 18 to 24 in. in diameter were considered 
necessary in small stations and the radiation owing to the poor quality 
of pipe covering then used was enormous. At the present time very few 
mains are put in of larger size than 14 in. I.D. and in some cases a 10- or 
12-in. main is considered sufficient. The drop in pressure between boiler 
and prime mover is considerably larger than formerly but the actual 
heat loss due to friction and radiation is very much less than it was. This 
reduction in pipe sizes also brought in great economies in the upkeep 
cost of the steam lines as with the high pressures carried at the present 
day it would be almost impossible to keep a 20-in. or 24-in. main tight 
under the conditions of actual service. 

Steam Speeds. — For years standard practice for the speed of steam 
in steam lines was 4,000 ft. per minute as the minimum, 6,000 as the 
average and 8,000 as the maximum. This was considered the standard in 
the days when 125 lb. steam pressure was carried without superheat. 
At the present time with 200 lb. pressure and superheat which may extend 
as high as 200°F. above the saturation temperature, the minimum steam 
speeds are much higher and very few engineers are using as the minimum 
speed less than 8,000 ft. per minute, the maximum in some cases running 
as high as 18,000 ft. with no bad results. Small branches should be 
figured for much lower speed. 

Details. — Starting from the boiler it is good practice today to connect 
the various boiler drums with what is known as a crossover header con- 
sisting of a steel casting with ball-and-socket joint connections to the vari- 
ous boiler drums and provided with a single outlet at the top from which 
the steam supply may be taken. This header is connected to the boiler 
drums by means of cast-steel nozzles which are riveted to the drums and 
which have on their upper flanges a ball-and-socket joint. On top of 
this crossover is placed some variety of automatic stop check valve 
which is required by the police regulations of certain cities. This stop 
check valve is made in many styles and performs a variety of functions. 
It is usually so arranged that when the pressure in the boiler drops 
below the main pressure the valve will shut preventing the steam from 
returning to the boiler. It is sometimes provided with an automatic clos- 
ing device so that when a steam pipe breaks and a sudden drop of 
pressure occurs in the main the valve will also shut. It is also provided 
with a hand closing and opening device. Such valves are shown in Figs. 
92 and 136. 

From the outboard flange of this valve the main boiler connection is 
taken to the main. This is of bent steel pipe with Van Stone flanges 



222 



ENGINEERING OF POWER PLANTS 



and is not usually larger than 10 in. for a 650-hp. boiler. Of late the sizes 
have been cut down to 8 in. and in some cases to 6 in. with very good 
results. Between this connection and the steam main a gate valve is 
always placed so that there may be two valves between the boiler drums 
and the steam main. This is good practice and the A.S.M.E. boiler code 
requires that every connection to the boiler shall have at least two valves 
between the boiler and the main. 

The steam main itself is divided into sections by means of gate valves 
some of which may be provided with hydraulic or electrical closing and 

opening devices so that they may be operated 
from a distance if necessary in cases of emer- 
gency. But all valves of this type should 
be provided with hand closing and opening 
gear as well as the mechanical gear. From 
the steam main at a convenient point the 
connection to the prime mover is made. 
At the steam main a gate valve is located 
and the lead is taken by the most direct 
methods with large bends to the throttle 
valve of the prime mover. It is not usual 
to place a second valve between the gate 
valve and the throttle on the prime mover 
as the automatic throttle and the throttle 
valve itself are considered as giving sufficient 
safety. 

Auxiliary Steam Piping. — It was formerly 
considered the best practice to have the 
auxiliary steam piping entirely separate 
from the main steam line and to this end a 
separate connection was made with a small 
valve to the end of the crossover pipe on 
every boiler, these connections being led 
into an auxiliary main of smaller size extend- 
ing across the rear of the boilers. This was an entirely separate system 
connected in no way with the main system. It has the customary two 
valves between the boiler and the main and a single valve at the main 
where the connection is made to the auxiliary, the throttle valve of the 
auxiliary engine acting as the second valve between the engine and the 
main. 

It is now considered better practice that the steam connections with 
those auxiliaries that are intimately connected with a prime mover should 
be taken directly from the steam connections of the prime mover near 
the throttle valve. In many of the latest stations this scheme has been 




Fig. 145.- 



-Automatic-stop check 
valve. 



PIPING 223 

carried out with very good results. This means, however, that a separate 
system must be provided in the boiler house for the feed pumps, fire 
pumps and other boiler room auxiliaries which is usually done by means 
of a similar separate piping system either taken from the boiler drums or 
else from certain points on the steam main that must always be in service. 
This is without doubt the best system where superheat is used in both 
prime niovers and the auxiliaries. 

High-pressure Drip Piping and Boiler Returns. — It is customary to 
install a drip system along the under side of a high-pressure steam main 
to return the water of condensation to the drip tank or boiler. This 
system is usually built up of small pipe with screw joints, pipe not over 
2 in. size being used for this purpose. Every fitting and valve in the main 
is tapped for a drip connection and a nipple is screwed in with a valve. 
Similar drips should be installed in the boiler connections next to the 
main. One of the drips on each boiler connection should be so arranged 
that it may lead into the ashpit of the boiler where it can be observed 
and this pipe is left open when the boiler is open for inspection showing 
that there is no steam next to the stop check valve. 

As the high-pressure drips are among the most important pipes in 
the station it is customary to make these of extra heavy pipe and a great 
deal of care is usually taken that all of the joints are tight and that the 
system is a substantial one in every respect. 

Feed-water Piping {High Pressure). — The high-pressure feed-water 
piping consists of all of the piping connecting the feed-water pumps with 
the boilers themselves. This includes the lines through the closed heaters 
when they are installed and also lines to and from the economizers. This 
pipe is almost invariably made of cast iron and for ordinary work does 
not exceed 8 in. in diameter even in the largest stations. Such pipe is 
usually from % to 1 in. thick with heavy flanges and raised seats. This 
piping system usually consists of a run of piping under each row of boilers 
from which a loop is taken up over each battery and down again connect- 
ing with the main on the other side. This loop is most always of 3-in. 
pipe and is provided at a point above the floor with a check valve and 
sometimes with a hose connection. The stop valves and check valves 
are usually of brass and the piping running over the boilers and between 
check valves is usually brass pipe, iron-pipe size, with brass flanges 
screwed on and sweated. In the middle of the battery above the boilers 
a gate valve is placed to separate the two parts of the loop, and brass 
fittings are inserted above the drums to provide for the 2-in. connections 
to the front ends of the boiler drums. These connections are bent brass 
pipe, iron-pipe size, and at the drum are provided with a combination stop 
and check valve so that any line may be thrown out of service if desired. 
This is not the standard arrangement, however. The standard consists 



224 



ENGINEERING OF POWER PLANTS 



Safety ftetease 
Valve 



Oil Operating 
Csriinder 



of a double line of 3-in. pipe extending up at the middle of the battery 
and connecting with a 2-in. line to each of the three drums. This line 
usually interferes with stoker installations or with the middle column 
which runs up between the two boilers of a battery and in large stations 
the installation is almost always made as first described. 

Each boiler maker usually has his own type of stop check valve at 
the drums and this valve is usually furnished with the boiler. The check 
valves and stop valves and the gate valve in the middle of the boiler over- 
head are usually also furnished by the boiler contractor. The piping 
below the main 3-in. stop valves is usually cast iron and is furnished by 
the pipe contractor. These mains run below the lines of boilers and are 

connected to the main feed line which may 
run the length of the station. This line is 
sometimes made as a ring header or closed 
loop. Sometimes it consists of a double 
line of mains with crossovers protected by 
gate valves which are usually of cast iron. 
Suitable air chambers for equalizing the 
pulsations are provided when reciprocating 
pumps are used. 

The use of steel pipe for feed- water lines 
is not to be recommended under any circum- 
stances. The hot pure water affects the 
material very badly causing pittings which, 
with certain impurities that are present, 
will probably destroy the pipe in a very 
short time. Cast iron seems to stand this 
sort of work much better than anything 
else which has been used and is very satis- 
factory. In many cases where steel has 
been used it has had to be removed within 
a very short time and cast-iron pipe 
substituted. 

Exhaust Piping. — The smaller sizes of exhaust piping up to 6 or 
8 in. are usuall}^ made of standard steel with cast-iron flanges for, say, 
50 lb. pressure. Between 8-in. and 30-in. spiral riveted galvanized 
pipe with steel flanges riveted on is commonly used; and riveted steel 
pipe for sizes above 30 in. Allowable speeds of exhaust steam in these 
pipes are very much larger than are allowable for pressure steam speeds, 
as high as 35,000 ft. per minute being permissible in certain cases. When 
a prime mover is arranged to be run continuously the exhaust connection 
to the condenser is usually made very short and of cast iron. The at- 
mospheric exhaust is connected into this pipe between the prime mover 




Fig. 146.- 



-Atmospheric 
valve. 



relief 



PIPING 



225 



and condenser and is provided with an atmospheric rehef valve which is 
arranged to open wide whenever the vacuum drops to a certain amount. 
Figure 137 shows a type of relief valve which has proved satisfactory 
in service. They are almost always valves of the globe type, pro- 
vided with weights and dashpots to prevent chattering and arranged 
for quick and full opening under operating conditions. Hydraulic 
devices are usually installed to allow opening or closing from a distance. 
The smaller apparatus, which is always run non-condensing, is provided 
with a direct exhaust pipe to the heaters where the steam is condensed 
at atmospheric pressure for heating the feed water. When turbine- 
driven auxiliaries are used and run non-condensing it is very important 
that there be no back-pressure at 
the exhaust nozzle of the turbine 
and great care should be taken 
that the exhaust pipes are suf- 
ficiently large and straightaway, 
that no pressure may be devel- 
oped at the exhaust nozzle. 

All exhaust piping should be 
laid out with a fall to the heater 
or else should be properly graded 
with drip piping of sufficient size. 
In a small plant where the ex- 
haust is allowed to go to the atmo- 
sphere, suitable mufflers should be 

installed at the top of the exhaust line to prevent noise. 
143.) 

Determining Pipe Sizes. — Many formulae have been used for 
determining pipe sizes for steam engines, but most of them are now 
obsolete. In Power for Jan. 19, 1915, F. W. Salmon presents results 
secured by plotting the necessary data from a large number of suc- 
cessful plants. 

HA — area of pipe bore in square inches, 
d = diameter of pipe bore in inches, 
W = average pounds of steam per hour, 
C = a constant for a given pressure in the pipe, 

K = a. constant = 




Fig. 147. — Anchor for steam main. 



(See Fig. 



then 



or 



W = Axe 

W 

K 



4 



d' = ^' 



Salmon presents the following tables for determining suitable pipe 
sizes: 



226 



ENGINEERING OF POWER PLANTS 



Vacuum, inches, Hg 





Constants 




C 


K 






r 28 


60 


39.2 






26 


84 


66.0 






24 


105 


82.5 






22 


122 


95.7 






20 
18 


134 

144 


102.0 






113.0 






16 


151 


118.6 






13 


162 


127.0 






6 


176 


138.0 




- 


I 


187 


147.0 




r 80 


267 


210.0 






100 


275 


216.0 


er sq. in.. . . 




125 
150 


284 
291 


223.0 






229.0 






175 


298 


234.0 






[200 


304 


239.0 



Commercial practice of a large central station is in accordance with 
the following table: 



Table Showing Approximate Pipe Sizes for Various Steam Flows at 200 Lb. 
Gage and 100°F. Superheat 



Size of pipe 


Maximum flow per hr., in lb. 


Maximum velocity per minute 


m 


720 


2,000 


2 


1,500 


2,600 


2K 


2,450 


3,000 


3 


4,500 


3,600 


4 


9,600 


4,500 


5 


17,500 


5,2C0 


6 


29,000 


6,000 


8 


60,000 


7,200 


10 


110,000 


8,400 


12 


175,000 


9,400 


15 O.D. 


275,000 


10,300 



Note. — Standard weight pipe. 



Grading of Pipe. — The slope of the pipe line should be toward the 
engine as water is often prevented from flowing back against the steam 
current. Drip pockets should be used in all fittings. The main Hne 
should pitch about 1 in. in each 10 ft. of run. Pipe fines always need 
draining. 1- to 2J^-in. drain pipes should be used. It is frequently 



PIPING 



227 



convenient to use the drip lines as bypasses instead of bypassed valves 
in high-pressure work. 

Expansion of Pipe. — The coefficient of expansion for ordinary steam 
pipe seems to be about 0.000006 of its length for each degree F. A rough 
and ready rule is to allow 3-^ in. for every 100 ft. for every 100°F. differ- 
ence of temperature. All pipe lines should be laid out to take care of 
this expansion, and to this end large radius bends should be employed 
wherever possible. It is usual to cut the pipe so it will be the right 
length when it is hot, making up the joints and pulling them together, 



.s_ 



^yyyyyyyyyAyyy^y 



^>>>>>>f-^'^^^^l^^^^^^^^ 



^//.-^/^^-//.-.-^/^^^^^^^^^^^ ^ 



I 



-0- 



FiG. 148. — Slip expansion joint. 




Fig. 149. — Wainwright 
expansion joint. 



SO that an initial stress is put in the cold pipe. When the pipe becomes 
hot, this stress disappears and the pipe will then be in equilibrium. 
Suitable hangers should be provided every 10 or 12 ft. to support the pipe 
in its proper place. These may consist of a band around the pipe with 




Fig. 150. — Baragwanath expansion joint. 



a rod hanger from some of the floor beams overhead, or the pipe may be 
supported from below on a roller. Anchors should also be provided at 
certain places so that the direction of expansion may be controlled. On 
very long lines sliding expansion joints become necessary, or the corru- 
gated-steel expansion joint may be used. 



228 ENGINEERING OF POWER PLANTS 

Pipe Coverings. — The best covering is 85 per cent, carbonate of 
magnesia, 1 in. thick on exhaust piping and 2 in. thick on high-pressure 
steam piping. This should be covered with 3^^-in. asbestos board and 
with sewed and pasted canvas. Removable flange coverings should be 
used. (See paper by McMillan, A. S. M. E., December, 1915.) 

Badly erected and leaky lines of steam piping may cause excessive 
waste. More steam (250 boiler hp.) can leak through a 1-in. hole in a 
steam pipe at 150 lb. steam pressure than one fireman would usually 
supply by steady coaling. 

Leaks in steam pipe are usually regarded as insignificant but they 
rapidly dissipate the heat generated in the consumption of a large amount 
of coal. Uncovered steam pipes also waste large amounts of coal and 
load the steam with water; water in the steam causes pounding or water- 
hammer in the pipes, which often produces serious results. 

A good steam covering will save some 80 per cent, of the loss of heat 
which takes place from the naked pipe and the investment in a good pipe 
covering will usually more than repay 100 per cent, interest. 

Cost of Piping. — The cost of piping in a steam power plant varies 
greatly with the type of installation and with the size of the plant, ranging 
all the way from $10 to $15 per rated horsepower installed in small 
plants, to $1.50 to $2.50 per rated horsepower installed in plants of from 
3,000 to 5,000 hp., using 125 lb. steam pressure. For turbine plants and 
engine plants using 175 to 200 lb. steam pressure with superheat, the 
piping cost for plants of 3,000 to 5,000 hp. will vary from $2.50 to $6. 
In large turbine plants using high-pressure steam and high superheat 
the cost may be in excess of $8 per horsepower. 

In one engine plant of 28,000 hp. the steam piping system cost $4.35 
per horsepower; the feed-water system, 30 cts.; the drip system, 25 cts.; 
the blowoff system, 10 cts.; the condensing water piping for jet condens- 
ers, 30 cts.; the house, fire and heating piping, 15 cts.; the jacket piping 
10 cts.; and the oil system and piping, 75 cts. This system used steam 
at 175 lb. pressure with no superheat. The use of steel fittings and the 
careful construction necessary for high-pressure superheated steam work 
has greatly increased the cost of steam piping. The one item of labor 
has practically doubled in the last 10 years. The list prices of pipe and 
fittings should be discounted from 50 to 75 per cent. 

An average cost formula for steam and water piping, valves and 
separators for compound condensing plants of 400 to 5,000 hp. capacity 
is 

Cost in dollars = 1,800 + 4.4 X i.hp. 

One consulting engineer reports the plant piping cost per indicated 
horsepower rating of the plant as follows : 



PIPING 



229 



Simple non-condensing 
Engine horsepower. , . . 
Cost per horsepower. . . 

Simple condensing: 
Engine horsepower . . . . 
Cost per horsepower. . . 

Simple condensing: 
Engine horsepower .... 
Cost per horsepower. . . 

Compound condensing: 
Engine horsepower. . . . 
Cost per horsepower. , . 

Compound condensing: 
Engine horsepower. . . . 
Cost per horsepower. . . 



10 
$8.30 



10 
$11.20 



40 
$7.70 



100 
$13.80 



800 
$6.25 



12 
$8.00 



12 
$11.00 



50 
$7.30 



200 
$11.20 



900 
$6.00 



14 
$7.60 



14 
$10.70 



75 
$6.10 



300 
$9.10 



1,000 
$5.75 



15 
$7.40 



15 
$10.20 



100 
$5.70 



400 
$8.00 



1,500 
$5.10 



20 
$6.70 



20 
$9.50 



500 

$7.40 



2,000 
$4.55 



30 
$5.70 



30 
$8.00 



600 
$6.80 



40 
$5.10 



700 
$6.50 



50 
$4.60 



75 
$3.90 



Eighty-five per cent, magnesia, 1 in. thick, costs in the neighborhood 
of 30 cts. per square foot in place. In general such covering costs about 
one-half lift price including labor. One writer states that one man will 
cover 100 ft. of straight pipe or 40 fittings per day up to 4-in. pipe size. 
About 4 in. the cost per 100 ft. of pipe length will be greater owing to 
the increased labor of handling. 

Exhaust Heads and Oil Extractors. — The atmospheric exhaust pipe 
which usually leads into the air above the roof of the station would be 




Fig. 151. — "Lagonda" oil filter and grease extractor. 



very noisy and likely to create a nuisance from the water entrained in 
the exhaust steam. To avoid the noise and save the water a muffler 
or exhaust head is fitted to the top of this pipe. This usually consists 
of a conical or cylindrical chamber two or three times the diameter of 
the pipe in which are placed wire screens and other baffles breaking up the 



230 



ENGINEERING OF POWER PLANTS 



flow of the steam and the organ pipe effect which would otherwise be pro- 
duced. Suitable baffles are also installed to catch the entrained water 
which is piped back to the heater or sump. 

Where the condensate from the exhaust steam from engines is to be 
used over again it is necessary to install a grease or oil extractor in the 
exhaust line. This usually consists of a set of baffles in an enlarged sec- 
tion of the pipe very similar in design to the steam separator, but of much 
larger size, as the velocities must be very low in order that the oil may be 




- ^ 


f 


-l^h 1 


\m^ 


Drain J 







Fig. 152. — Exhaust head. 



deposited. It should be remembered that if the oil becomes emulsified or 
volatilized it will be practically impossible to catch it. In such cases it 
will be better to change the quality of the oil or throw away the water. 
There are also grease extractors made to remove the emulsified oil from 
water by means of electrical currents. These machines are good in 
their way, but are costly and take up a great deal of space. Another 
type of grease extractor is the pressure fflter with cartridges of absorptive 
material, such as excelsior. These machines are also bulky and not 
much used. 



PIPING 



231 



Steam Traps. — The high-pressure engine drips should, if possible 
be led back direct to the boiler, but if this is not possible, the next best 
place is the open heater. The low-pressure drips contain more or less 
oil, and should be thrown away. If, however, it is necessary to save 
them, a steam trap may be used which will lift the returns to a sufficient 
height to enable them to flow by gravity to a heater or storage tank. 
Steam traps may also be used in the high-pressure line, returning the 
condensed water to the boiler direct. The steam trap is usually a closed 
container provided with a small valve controlled by a float or bucket in 
such a manner that when the container becomes full of condensed water a 
small valve is opened and the steam pressure forces the condensate 




Fig. 153. — Steam trap, float type. 



through the pipes to its destination. These small valves require an 
enormous amount of care to keep tight, otherwise the high-pressure steam 
blows through the trap and is a continual waste. Use as few traps as 
possible. The receiver with pump is a better device than the trap and is 
used in the better class installations. 

Steam Loop. — A much better device than the trap for returning drips 
to the boiler is the steam loop of which there are a number of varieties. 
In general the system consists of a riser from the drip point, a length of 
uncovered pipe slightly sloping toward the discharge end and a drop leg 
connected to the mud drum of the boiler with a check stop valve and 
bleeder. The condensation and cooling in the uncovered horizontal 
pipe creates a sufficient drop in pressure to bring mixed steam and water 
to the upper level of the apparatus where it cools and by its weight forces 
itself past the check valve into the mud drum. The steam loop is some- 
what modified in the larger systems but although successful when well 
installed is not as good a system as the receiver and pump. 

Steam Separators. — The separator is an enlargement of the piping 
system in which the steam velocity is reduced aiid the particles forced 



231a 



ENGINEERING OF POWER PLANTS 



to travel in a zigzag direction against surfaces, corrugated or provided 
with lips to catch and retain the liquid particles which run down in the 
wake of the lips out of contact with the steam into a receiver. Some 
separators have screen baffle, others grids, but all embody the two 
principles, change of direction and reduction of velocity. Separators 
are built with either cast-iron, cast-steel, or riveted-steel shells but the 
heads are always castings. 

Although absurdly high efficiencies are claimed by manufacturers of 
steam separators, efficiencies which cannot be realized in commercial 




Fig. 154. — Cochrane separator. 

practice, yet no separator should be retained in service that does not 
remove at least 70 per cent, of the water carried by the steam approach- 
ing the separator. 



PROBLEMS 

61. A 6-in. pipe line 150 ft. long carrying steam at 125 lb. gage pressure, was put up 
without expansion joints. x\t the end of the 150-tt. run the direction of the pipe was 
changed abruptly 90° and the pipe rigidly held in the new direction. Close to the 150- 
h. point several short K-in. connections were tapped into the 6-in. main. As soon as 
steam was turned on the 6-in. ell was ruptured and every connection torn off. Why? 
How much did the pipe move at the point in question? 

62. Determine the proper steam and exhaust pipe sizes for a 325-i.hp. non-condens- 
ing Corliss engine. What would be the pipe sizes if this engine were designed to run 
condensing? 

What would be the sizes for a 6,000-hp. condensing engine? 

63. A 100-hp. Corliss compound condensing engine requires the following steam 
per indicated horsepower-hour. 

Percentage of load , 25 50 75 100 125 

Pounds steam per indicated horsepower-hour. ... 32 24 21 20 20.5 



PIPING 2316 

If the steam pressure is 100 lb. gage, what size steam and exhaust pipes ought the 
engine to have? What is the velocity of the steam in the pipes for the various loads 
on the engine? 

64. Calculate the velocities in the various pipes as given by Salmon's formula. 
Plot them with pressures as abscissae. Deduce the equation to the curve. Plot the 
curve 

36,000 

and compare. 



CHAPTER XI 
COAL AND ASH HANDLING 

Coal Handling. — For small plants coal is usually hauled by wagons 
and dumped in the boiler room in front of the boilers, but it is better 
practice, even in these small plants, to provide a pocket above the boilers 




Fig. 155. — Coal handling machinery Williamsburg Power House Transit Develop- 
ment Co., Brooklyn, N. Y. 

with some means for getting the coal into it. The coal may be dumped 
from the car or wagon into a small receiving hopper, which feeds a travel- 
ing belt, conveyor bucket or elevator system, which transfers the coal to 
the overhead pocket. In some stations the car is unloaded by means of 

232 



COAL AND ASH HANDLING 



233 



a grab bucket on a telpher system which transfers the coal, a bucketfull 
at a time, from the car or wagon to the coal pocket. 



Operating (Jear 



Coal Elevator 

Coal. Weighing 

and Distributing 

Crane 



Coal Bin 
over each Producer 

Operating Gear 
for Producer 

Gas Producer, 
ughes Self Cleaning 



Coal Car 




!FiG. 156. — Typical coal-handling apparatus for gas producers or boilers. 



Where it is not possible to install a coal pocket it is customary to have 
a storage pile in the neighborhood of the fire room. Industrial railway 
tracks are run from the pile to the boiler fronts and small cars may be 



234 



ENGINEERING OF POWER PLANTS 



loaded either by hand or by a small locomotive crane and run along the 
tracks in front of the boilers, the hand-firing being done direct from the 
cars. 

This outside coal storage has been adopted for a number of larger 
stations, but small hoppers are provided above each boiler capable of 
holding 2 or 3 tons of coal and a car system, or telpher system, has been 
installed from the coal pile to the fire room to keep these hoppers full. 

The design of coal-handling machinery depends largely on local con- 
ditions. In one station of 15,000 hp. the location is on a hillside, the 
coal supply being obtained by wagons which drive onto the roof of the 




ConTeyor to 
Storage PUe 



Fig. 157. — Typical coal-handling tower, one-man type. 

station and dump their coal directly into the coal pocket. At Carville, 
near Newcastle, England, the railroad siding is extended over the roof of 
the boiler house and the coal is delivered direct from cars to pocket. 

Most of the larger stations in the Eastern States receive their coal by 
water. The coal is removed from the boats by means of clamshell buck- 
ets, often as large as 2 tons capacity, which are hoisted at once to a maxi- 
mum height required for delivering the coal. This amounts in some 
stations to a hoist of 140 ft. The coal is dumped from the clamshell 
bucket into a receiving pocket and then passed through a crusher which 
reduces the coal to the proper size for firing. From the crusher it goes into 
the cars of a cable railroad or conveyor, which delivers it to the various coal 



COAL AND ASH HANDLING 



235 



pockets from which large downtakes lead to each stoker or firing door. 
The cable railroad is usually the cheapest conveyor to install, maintain 
and operate. Next comes the traveling belt. The bucket conveyor is the 
most costly of the three. 

Forty to 50 tons of coal may be unloaded per 8-hr. day by one man. 

One man has fired as much as 16 tons of coal per watch of 8 hr. 

Cost of Coal Handling. — In small plants the cost of coal handling may 
be as large as 40 to 45 cts. per ton fired. Where machinery is installed 
the cost drops with careful design and increase of size of plant to the 
neighborhood of 8 to 12 cts. per ton with good sized plants. For the larger 
of the central stations this cost should not exceed 4 cts. per ton. The 
cost of stacking in well-designed storage piles should not exceed 2 cts. per 
ton and the cost of reclaiming will be about the same. It should be 
remembered that in small plants a good man and one mule will handle a 
considerable amount of coal at an exceedingly cheap rate, and in most of 
the smaller plants it will not pay to install coal-handling machinery. 

An idea of the saving to be secured by mechanically handling the coal 
may be obtained from the following figures: 

A plant of 7,500 hp. in boilers was operated for some time without 
coal-handling machinery other than small hand cars which were loaded 
by hand from railway cars outside of the building, and which were then 
hauled up a straight incline to the boiler house, so that the fuel could be 
dumped in front of the furnaces. 

The coal-handling machinery later introduced was so arranged that 
the coal was only handled by hand in shoveling it out of railway cars onto 
the conveying system. 



Wages 



Tons 
burned 



Cost per 
ton 



Hand operation: 

16 firemen and 1 helper, 

11 coal and ash men. Ash removed by contract 
Mechanical operation: 

3 firemen and 2 helpers, 

11 coal and ash men, 2 conveyor men 



$981.80 
634.66 

287.75 
654.50 



4,292 



6,975 



$0,229 
0.1478 

0.041 
. 0938 



The saving in wages of firemen and helpers amounted to 18.8 cts. per 
ton, which is 82.1 per cent, or $1,311.30 per month. 

The saving on coal and ash handling is 5.4 cts. per ton, which is 
41.4 per cent, or $376.55 per month, or a total saving of $1,687.85 per 
month or over $20,000 per year. 

If the coal did not have to be shoveled from coal cars onto the conveyor 
in this plant the saving on labor might be even greater. 



236 



ENGINEERING OF POWER PLANTS 



The total cost of handling coal from coal car to ash car in large cen- 
tral stations is roughly 10 to 18 cts. per ton. 

Letters from owners of about 600 boilers to Mr. R. S. Hale of the 
Steam Users' Association, indicate that it costs to move coal by hand 
(wheelbarrow) about 1.6 cts. per ton-yard up to distances of 5 yd., then 
about 0.1 ct. per ton-yard for each additional yard. 

One man, besides a night man, can run an engine and fire up to about 
10 tons of coal per week. 

One man, besides an engineer and night man, can fire up to about 
35 tons per week. 



Settling Chamber 



Special C.I.Tee and Plug 

-Flanged 
Plug 




Fig. 158. — Diagrammatic view of pneumatic ash-conveyor plant, Armour Glue Works, 

Chicago, 111. 

Two men, besides an engineer and night man, can fire up to about 
80 tons per week. These figures assume that the night man does all he 
can of the banking, cleaning and starting. 

Mr. Hale further reports that mechanical stokers save 30 to 40 per 
cent, of labor in plants burning from 50 to 150 tons per week, and save 
no labor in small plants. 

Boiler attendants were paid about $1.50 per day of 10 or 12 hr. 

Average cost of firing coal was reported to be 48 cts. per ton; maximum, 
71 cts. per ton; minimum, 26 cts. per ton. 

Ash Handling. — In small hand-fired plants and in most of the older 
plants no ash pockets were provided under the grates, the firemen pulling 
the ashes out of the ashpit with a hoe and then shoveling them into ash 



COAL AND ASH HANDLING 237 

cans, wheelbarrows or cars for removal. Where the power plant has a 
basement ash hoppers allowing the storage of about 8 hr. ashes are usu- 
ally provided. These hoppers have suitable gates at the bottom, through 
which the ashes may be dumped into steel dump cars which are hauled 
by an electric locomotive outside the station. In the country the ashes 
are generally used for filling in adjoining land; in the interior cities they 
are usually valuable, in some cases bringing as high a price as 50 cts. per 
cubic yard. Where they cannot be used for these purposes the dump 
cars deliver into a skip or ash hoist which delivers the ashes into a pocket 
from which they may be delivered into boats, cars or wagons for disposal. 
At the Armour Glue Factory in Chicago is installed a pneumatic ash sys- 
tem, taking care of the ashes from 22 B. & W. boilers of 300 hp. each. In 
this installation an 8-in. cast-iron pipe is run along the front of the ash hop- 
pers which are large enough for 24-hr. storage. The hopper is provided on 
an 8 by 12-in. aperture in the pipe and the ashes are pulled from the ash 
hopper into the pipe by hand. A vacuum of from 10 to 15 in. of water 
is maintained in the pipe by an exhauster of the Conner sville double- 
impeller type placed at the outboard end of the 8-in. line. In front of 
the exhauster a separator is placed similar in principle to the standard 
shaving separator and discharged through a valve in the bottom into the 
ash pocket. With this system the ashes are conveyed horizontally 200 
ft. around numerous bends, and vertically 70 ft. before being discharged 
into the hopper. The ashes must be dry and all large lumps and clinkers 
must be broken up. The operation is by one man and is said to take not 
over 2 hr. per day. 

Traveling belts and bucket conveyors have also been used for hand- 
ling ashes, but the upkeep on this apparatus is very large indeed. 

Cost of Ash Handling. — The cost of getting the ashes out of the sta- 
tion and into the ash pocket will vary from 25 cts. per ton of coal fired in 
small stations to as low as 4 or 5 cts. per ton of coal fired in very large 
stations with well-designed apparatus. The cost of removing ashes 
varies with the locality and may be a source of revenue under certain 
conditions. No figures can be given for the maintenance of ash-handling 
plants, but as a general rule, the maintenance will be at least as large as 
the labor cost, as ash-handling machinery wears out rapidly. The cost 
of ash handling varies also with the kind and quality of coal, being larger 
as the percentage of ash increases, and much larger with clinkering coal. 

Coal Storage. — It is usual in power stations to provide coal pocket 
space for from 7 to 10 days' supply of coal. This, however, is insufficient 
for a central station and further storage must be provided outside of the 
station. This usually consists of a coal pile, ranging from 10,000 to 
200,000 tons capacity, depending on the size of the central-station system, 
it usually being considered that from 3 to 6 months' supply is sufficient 



238 ENGINEERING OF POWER PLANTS 

to insure continuity of operation under all circumstances. These piles 
are provided with stacking and loading machinery and are of two general 
types, one in which the pile is spanned by a bridge carrying the loading 
and unloading machinery, and the second type in which the pile is made 
by means of trestles and cable cars, while the unloading is done by means 
of locomotive cranes and the cable-car system. A third type, largely 
used by the hard-coal railroads, consists of conical piles about 400 ft. in 
diameter and 90 ft. high, in which the small sizes of anthracite coal are 
taken to the top of the pile by means of inclined flight conveyors, and the 
reclaiming is done by a movable horizontal flight conveyor. 

H. H. Stoek in an extensive discussion^ of the storage of bituminous 
coal presents the following summary of conclusions: 

Based upon the facts and information hereinafter presented certain definite 
statements are justified regarding the reasons for storing coal, the kinds and 
sizes of coal to be stored, the methods of piling, and other factors entering into 
the problem of successful coal storage. These represent very largely a digest 
of opinions expressed by many persons who have had experience in storing coal 
and, it is believed, constitute a comprehensive statement of the present knowledge 
of safe coal storage practice. These conclusions are presented as follows: 

1. It is practical and advantageous to store coal not only during war times 
but also under normal conditions, at the mine, near the point at which it is to be 
used, or at some intermediate point. If possible, it should be stored near the 
point of consumption to avoid rehandling and the resultant breakage. 

The reasons for storing coal are : 

(a) To insure the fuel consumer a supply of coal at all times. 
(6) To take advantage of low freight rates, or of low prices for coal at certain 
seasons of the year. 

(c) To permit the railroads to utihze their cars and equipment to the best 
advantage. 

(d) To maintain a uniform rate of production at the mines. 

2. Kinds and sizes of coal which may be safely stored: 

(a) Although it is undoubtedly true that some coals may be stored with 
greater safety than others, the danger from spontaneous combustion is due more 
to improper preparation and piling of coal than to the kind of coal stored. 

(b) Most varieties of bituminous coal may be safely stored if of proper size 
and if free from fine coal and dust. The coal must be handled in such manner 
as to prevent excessive breakage and the consequent production of much fine 
coal and dust when being placed in storage, because spontaneous combustion is 
due mainly to the oxidation of the coal surface. The danger of spontaneous 
combustion in storing coal is very greatly reduced, if not entirely eliminated, 
by storing only lump coal from which the dust and fine coal have been removed. 
Of two coals, the one which is least friable should be chosen for storage purposes 
because less dust and fine coal will be produced in its handling. All varieties 

1 "The Storage of Bituminous Coal," H. H. Stoek, Circular No. 6, Engineering 
Experiment Station, University of Illinois, 1918. 



COAL AND ASH HANDLING 238a 

of bituminous coal can be stored under water, since water excludes the air and 
prevents spontaneous combustion. 

(c) Fine coal or slack has sometimes been safely stored in cases in which 
air has been excluded from the interior of the pile. Exclusion of air from the 
interior may be accomphshed (1) by a closely sealed wall built around the pile 
or (2) by close packing of the fine coal. Any pile of slack requires careful watch- 
ing to detect evidences of heating and means should be provided for moving the 
coal promptly if heat develops. The only .absolutely safe way to store slack or 
fine coal is under water. 

(d) Many varieties of mine run coal cannot be stored safely because of the 
presence of fine coal and dust mixed with the lumps. 

(e) Coal exposed to the air for some time may become "seasoned" and 
thus may be less liable to spontaneous combustion because of the oxidation of 
the surfaces of the lumps of coal, but opinions are by no means unanimous on 
this point. 

(/) It is believed by many that damp coal or coal stored on a damp base is 
peculiarly liable to spontaneous combustion, but the evidence on this point is 
by no means conclusive. It is safer not to dampen the coal when or after it is 
placed in storage. 

3. The effect of sulphur on spontaneous combustion: 

It has been shown by experimentation that the sulphur contained in coal 
in the form of pyrites is not the chief source of spontaneous combustion, as was 
formerly supposed, but the oxidation of the sulphur in the coal may assist in 
breaking up the lumps of coal and thus may increase the amount of fine coal 
which is particularly liable to rapid oxidation. Even this opinion is not un- 
animously endorsed. In spite of experimental data showing that sulphur is 
not the determining element in spontaneous combustion, the opinion is wide- 
spread that, if possible, it is well for storage purposes to choose a coal with a 
low sulphur content. 

4. Method of piling coal: 

(a) To prevent spontaneous combustion, coal should be so piled that air 
may circulate freely through it and thus may carry off the heat due to oxidation 
of the carbon, or it should be so closely packed that air cannot enter the pile and 
oxidize the fine coal. 

(6) Stratification or segregation of fine and lump coal should be avoided, 
since an open stratum of coarse lumps of coal provides a passage through which 
air may enter and come in contact with the fine coal, thus oxidizing it and starting 
combustion. 

(c) If space permits, low piles are preferable since in low piles the coal is 
more fully exposed to the air and is better cooled than in high piles and in case of 
heating it can be more readily and quickly moved. A disadvantage of high 
piles lies in the greater difficulty of moving the coal quickly, if necessary. The 
idea that a high pile causes heating at the bottom is erroneous, since as many 
fires take place near the top as near the bottom, and as many near the outside 
as near the interior of the pile. If possible, the coal should be divided by alley- 
ways so as to facihtate rapid loading out of the coal in case of necessity, and 
so that an entire coal pile may not be endangered by a local fire. 



2386 ENGINEERING OF POWER PLANTS 

{d) Much of the attempted ventilation of coal piles has been inadequately 
done through the use of only an occasional ventilation pipe, which has been 
not much more than a place in which to insert a thermometer. The practice of 
placing ventilating pipes closely together has been used in Canada and is re- 
ported to be effective. 

(e) Water is an effective agent in quenching fire in a coal pile only if it can 
be applied in sufficient quantities to extinguish the fire and to cool the mass. A 
small quantity of water is not effective. Unless there is an ample supply of 
water thoroughly to quench the fire and to cool the pile, it is very dangerous to 
add any water to a coal pile. 

(/) Coals of different varieties should if possible not be mixed in storage, for 
the coal possessing the greatest tendency toward spontaneous combustion may 
jeopardize the safety of other varieties not so liable to spontaneous combustion. 

5. The effects of storage upon the properties of coal: 

{a) The heating value of coal as expressed in B.t.u. is decreased very little by 
storage, but the opinion is wide-spread that storage coal burns less freely than 
fresh coal. Experiments indicate tha.t much of this deficiency may be overcome 
by keeping a thinner bed on the grate and by regulating the draft. 

{h) The coking properties of most coals seem to decrease as a result of storage, 
but coals vary greatly in this respect. 

(c) The deterioration of coal stored under water is negligible, and such coal 
absorbs very little extra moisture. If only part of a coal pile is submerged, the 
part exposed to the air is still Kable to spontaneous combustion. 

6. Additional precautions: 

{a) The best preventive of loss in coal storage is regularly to inspect the pile. 
If the temperature reaches 150°F.,. the pile should be carefully watched and if the 
temperature rises to 175 or 180°F. the coal should be removed as promptly as 
possible. The coal should be thoroughly cooled before being replaced in storage. 

(6) Storage appliances and arrangements should be so designed as to make 
it possible to remove the coal quickly if necessary, and coal should not be stored 
in large piles unless provision is made for loading it out quickly. 

(c) Pieces of wood, greasy waste, or other easily combustible material mixed 
in a coal pile may form a starting point for a fire, and every effort should be made 
to keep such material from the coal as it is being placed in storage. 

{d) It is important that coal in storage should not be subjected to such 
external sources of heat as steam pipes, because the susceptibility of coal to 
spontaneous combustion increases rapidly as the temperature rises. 

Warning: Special emphasis is laid upon the fact that safety in the storage of 
coal depends upon a very careful and thorough consideration of and attention to 
details referred to in the foregoing. Lack of attention to these details and lack of 
care in handling will in many cases result in losses due to dangerous fires. Do 
not undertake to store coal until you are sure you know how to do it properly and 
safely. 



CHAPTER XII 

THE STEAM POWER PLANT 
OPERATING COST 

Design of Power Plant. — No better service can be rendered the non- 
expert about to construct a power plant than to advise him to engage a 
capable engineer to design the plant and to superintend its installation. 

Methods of Buying Apparatus. — 

(a) Bids. 

(6) Have reputable manufacturer build it and pay what he asks. 

(c) Have engineer state in specifications requirements of apparatus 
wanted, permitting manufacturer to vary details enough to enable him 
to use standard designs. 

(d) Have engineer design the whole plant in detail buying standard 
apparatus where possible but developing new designs to meet new con- 
ditions. 

Location. — The most important factors governing the location of the 
power plant are: 

(a) Availability of water supply, especially for condensing. 
(6) Economical handling of fuel and ash. 

(c) Storage capacity for fuel. 

(d) Ease of power distribution. 

(a) The supply of water must be guaranteed and must be abundant. 
Wells do not usually furnish desirable water for boiler purposes, lake or 
river water being preferable. Ferranti states: 

"The water supply is enormously important today and I see no method so 
long as the converting process is thermal, that is to say, where there is a rise and 
a reduction in temperature, where the cooling water will not play a most impor- 
tant part." 

(6) If possible, the boiler house should be so located that coal can be 
delivered directly from boats or cars to the storage bins. If the grade 
can be so arranged as to avoid elevating the coal, a saving of from 25 to 
50 cts. per ton may often be effected. 

(c) Ample coal storage capacity should be provided to serve in times 
of strikes, blockages, etc. 

(d) This depends upon the character and purpose of the plant. Pro- 
visions should always be made for future enlargements and extensions. 

Constructions. — The type of building is determined by the price of 
land and the available space. The engine and boiler house should be 

239 



240 



ENGINEERING OF POWER PLANTS 



separate from the other buildings, to avoid danger from fire and to pre- 
vent troubles from vibration. 

Where the ground is not too expensive the entire plant may be on one 
level. In this case a one-story building with brick walls, steel-truss roof, 
and cement floor is most common. A well-drained and well-lighted 
basement should be provided if the plant is large for pipes, condensers, 
ash hoppers, traps and such apparatus as is necessary below grade. In 
large plants basements are often 20 to 25 ft. in the clear. 

-• Rem forced Cinder Concrete 







Fig. 159. — Spy Run Power House, Ft. Wayne and Northern Indiana Traction Co. 

Where ground is expensive it is necessary to build in stories, but this 
practice should be avoided when possible. 

It is a question whether engines or boilers should be placed above. 
Formerly the boilers were placed above the engines, but of late the plan 
has been reversed. 

All pumps, heaters, etc., should be on the main floor where practicable 
for the sake of light and cleanliness. The engines and boilers should be 
in separate rooms with a tight partition between to keep dust and 



THE STEAM POWER PLANT 



241 




:=! 
fl 

0) 

.2 

c3 

o 
-^ 

bD 



242 ENGINEERING OF POWER PLANTS 

moisture from the engines. All power stations should be fireproof. 
Wooden floors should not be used as the fire risk is too great. 

Arrangement. — The boilers should be located in batteries of two along 
the side of the boiler house opposite the coal supply, and each battery 
should be easily accessible on all sides. 

Special attention should be paid to facilities for cleaning shell, tubes, 
flues and combustion chambers. 

It is always desirable to have at least one spare engine in case of 
breakdowns. 

If there are several engine units it is more economical to have dift^erent 
sizes, that the engine power may be adapted to the load at any time 

The engines should be arranged with steam nozzles in line and con- 
necting with the horizontal header. If there is no basement, all exhaust 
pipes and drips should be carried in conduits under the floor and be easily 
accessible Have no pipe where it cannot be readily seen and handled. 

If the engines are non-condensing, the exhaust steam should be run 
first through a feed-water heater and the balance of the heat used for 
warming the building. If the vacuum system of heating is used, there 
will be less back-pressure on the engine. 

There should be one main feed line connecting the pumps with all the 
boilers. It is also well in small plants to have an injector connected di- 
rectly to each boiler to use in emergencies but this is too expensive for 
boilers above 50 hp. Some provision must be made for filling the boilers 
when cold either from the city mains or by hand pumps. 

The fundamental requirements of station systems are reliability, 
accessibility and durability. The engineer is concerned in the design of 
stations that will never require a shutdown of the entire system. The 
conditions of service must determine the system. If the service is 24 hr. 
a day, running for 8 hr. at half load only, then the system should provide 
for repairs being made, at the same time maintaining the capacity. If 
the station is required to generate at all times two-thirds of its total capac- 
ity, the plant should not have less than three units all of the same size. 

No unit should be so large that the station cannot be operated without 
it by overloading the other machinery to the permissible limit. 

For good service and economy in large central stations all units should 
be of the same size and the number of generating units should not be less 
than five nor more than eight, one unit in reserve, the others for carrying 
the load. 

In any case the original installation should be for a two-division, three- 
division or four-division plant with provision for future divisions. If the 
plant is to be a two-division plant it may be built with two units, each of 
a capacity slightly larger than the minimum load conditions demand, and 
the future unit may be made twice the capacity of these smaller ones. 



THE STEAM POWER PLANT 



243 




244 ENGINEERING OF POWER PLANTS 

This arrangement of units would be permissible in a plant which ordi- 
narily delivers onlj^ half of the power called for on Sundays, holidays, etc. 
It has been found ordinarily that a three-division plant is more suitable 
for permitting repairs to be made and also requires less investment for 
reserve capacity. If the plant is to be a three-division plant, the boilers 
should be in three divisions, say, 6, 9, or 12 in number. 

The auxiliaries should be in pairs, not necessarily together, but each 
sufficient for the entire plant, and they should be connected to the differ- 
ent divisions so that when one division is out of service the other auxiliary 
will be on operating division. 

Let it be assumed that a station requires three units for an output of 
two-thirds of the total capacity of the units and later will require an addi- 
tional unit. There is but one solution for the problem under these 
conditions and that is that the station shall ultimately be a four-divi- 
sion plant for output of three-quarters of the total capacity of the units. 
The boilers must be arranged in three units so as to allow one to be out 
of condition for cleaning and repairs. 

Assuming the engines to be of 2,000 hp. each, then two 500-hp. boilers 
would be required for each engine, but by assuming three engines of 
2,000 hp. each or a total of 6,000 hp. there would be 3,000 hp. in boilers 
to be divided into five units, so as to allow one boiler to be out of service. 
This would give five 600-hp. boilers. If the fourth engine unit is likely 
to be ordered before the three units are called upon to carry full load for 
a large part of the time it would be safe to estimate on 8,000 hp. of engines 
or 4,000 hp. of boilers, or seven boilers, each of 555 hp., which is a some- 
what better arrangement for the four-unit plant. 

Types of Station Design. — In the United States, where fuel has as a 
rule been reasonably cheap, the standard type of power station includes 
the boiler and engine with steam-driven auxiliaries. Economizers are 
very rarely used and the auxiliaries are run non-condensing, the exhaust 
steam being led to a heater and used for heating the feed water. This 
may be termed standard American design, and exceedingly good results 
may be obtained from it. 

In Europe, where coal is as a rule poorer and more costly than in 
America, and where interest charges have been considerably less, another 
type of station is more usual. Economizers are the rule and usually at 
least one-half as much surface is furnished in the economizer as in the 
boilers. The auxiliaries are driven direct from the prime mover or by 
electric motors, and no feed-water heaters are used because of the lack 
of available exhaust steam. The condensate is used over again, being 
pumped directly into the economizers. Such stations, when well de- 
signed, are capable of exceedingly good economy, but apparently no 
better than is given by the American type of plant. 



THE STEAM POWER PLANT 



245 




246 



ENGINEERING OF POWER PLANTS 



There are a number of American plants following to some extent the 
European types, but differing from them widely in the types of apparatus. 
In these plants both economizers and feed-water heaters are present, 
together with a number of other heat-saving devices. The auxiliaries 
are electrically driven from current supplied by a separate auxiliary unit, 
which has a jet condenser, in which the feed water of the station is used 
as the condensing water. There are many modifications of this type 
possible, and notable examples exist in the Conners Creek station of the 
Detroit Edison Co. and the Cleveland Municipal Plant. It is doubtful 
whether better results under similar conditions will be obtained by this 
type of station. 

I \<ToSfac^ 





mmatm nmR EXHAm t 



SURFACE .-■*' 
C0MDEN5ER 

COMBINATION^ 

CONDENSATE 

AHDAIRPUMP] 

mLsrtm 



HURLINQrWATHi RESERVOIR 



ECONOMIZERS 



5j-eam -from 
"Auxiliams 



rwE 



BpILER^ 




k=Dl5CHAR6E TUNNEL 
B^/NTAKE TUNNEL 



Fig. 163. — Diagram of steam and. water circuits Northwest Station, Commonwealth 

Edison Co., Chicago, 111. 

These three types may well be represented by the apices of an equi- 
lateral triangle; between them hes the whole field of the many variations 
which occur in design. Given the same load factor and use factor and 
with equally careful design, it is probable that similar economic results 
may be obtained from any type of plant, but to secure these results the 
design must be of the very best and the local conditions must be good. 
In particular the design must be suited to the local conditions and the 
type of fuel procurable in that locality. 

A fourth type of power station, which perhaps under modern condi- 
tions might be as economical as any, is the power plant of the steamer 
Inch Dene, a 10-knot freighter using Scotch marine boilers, superheated 
steam, multiple expansion engines, with the auxiliaries driven from the 
engine itself. The economical results from these ships have been exceed- 
ingly good, but it should be remembered that the use factor in this case 



THE STEAM POWER PLANT 



247 



is practically 90 per cent. Particulars of a test of this vessel may be 
found in Marine Engineering, vol. 6, p. 332. 

At the present time there is renewed agitation for the use of higher 
pressure steam, and a number of manufacturers are ready to supply boil- 
ers designed to furnish steam at 600 lb. pressure and 200° superheat. 
The turbine manufacturers are prepared to offer turbines to utilize this 
high-pressure steam. Whether these changed conditions will result in 
a new type of station cannot be stated, but it is certain that additional 
operating economies may be secured, although the total economy, when 
fixed charges are considered, may not be much better. 

It is not probable that any one type of station will become standard, 
but that the development of the three types with their variations will 
proceed along similar lines until a change takes place in our method of 
generating power. 

Cost of Buildings. — The estimated cost of buildings is most readily 
determined on the basis of cost per square foot of floor space or cost per 
cubic foot of space for the entire building. 

The following figures represent the averages of several quotations : 



Cost per 
square foot, 



Cost per 

cubic foot, 

cents 



Mill construction 

Fireproof stores, factories and warehouses with brick, con- 
crete, stone and steel construction 

Concrete or reinforced-concrete shops, factories and ware- 
houses 

Plain power houses with concrete floors and with brick and 
steel superstructure 

Power houses under city conditions with superior archi- 
tectural details . . . , 



0.80-1.10 
2.00-3.00 
1.25-1.75 
2 . 00-2 . 75 
3.00-4.50 



6.5- 8.5 

14.0-25.0 

8.0-16.0 

9.0-12.0 

15.0-30.0 



A consulting engineer of large experience finds the cost of boiler houses, 
engine houses and coal pockets to run approximately as follows when 
based on the cost per engine horsepower installed. 

Cost of Buildings per Engine Horsepower 



Simple non-condensing engines 

Engine horsepower 

Boiler house, cost per hp 

Engine house, cost per hp 

Coal pocket, cost per hp 

Simple condensing engines: 

Engine horsepower. 

Boiler house, cost per hp 

Engine house, cost per hp 

Coal pocket, cost per hp 



10 
$37.15 
4.80 
20.00 



10 

$33.70 

14.40 

19.00 



12 
$33.00 
4.35 
18.00 



12 

$29.60 

12.60 

17.90 



14 
$30.00 
4.00 
16.00 



14 

$27.50 

11.30 

16.60 



15 

$28.50 

3.90 

15.00 



15 

$26.20 

10.90 

15.80 



20 
$24.50 
3.30 
13.70 



20 
$21.60 
8.60 
13.60 



30 
$20 . 50 
2.75 
11.00 



30 
$18.20 
7.75 
11.00 



40 
$18.00 
2.50 



50 
$16.00 
2.30 
8.30 



75 
$13.00 
2.15 
6.00 



248 



ENGINEERING OF POWER PLANTS 



Cost of Buildings per Engine Horsepower. — (Continued) 



Engine horsepower 

Boiler house, cost per hp 

Engine house, cost per hp 

Coal pocket, cost per hp 

Compound condensing engines: 

Engine horsepower 

Boiler house, cost per hp. \ 
Engine house, cost per hp. / 
Coal pocket, cost per hp 

Engine horsepower 

Boiler house, cost per hp 

Engine house, cost per hp 

Coal pocket, cost per hp 



40 
$16.00 
6.40 
8.70 



100 

$28.50 
5.70 

700 
$5.35 
6.30 
2.10 



50 
$14.80 
5.35 
8.50 



200 
$24 . 00 
4.00 

800 
$5.00 
5.60 
2.05 



75 
$11.30 
4.90 
6.30 



300 
$11.20 
11.20 
3.10 

900 
$4.70 
5.35 
1.95 



100 

$9.70 
4.30 
5.70 



400 
$8.00 
9.35 
2.60 

1,000 

$4.55 

5.00 

1.80 



500 
$6.40 
8.50 
2.40 

1,500 

$4.10 

4.75 

1.75 



600 
$5.70 
7.20 
2.25 

2,000 

$3.95 

4.55 

1.60 



Incidentals. — In erecting a power plant, there are always a lot of mis- 
cellaneous items that add to the total expense but which are very difficult 
to determine before the installation is made. These always amount to 
considerably more than anticipated, usually averaging in the neighbor- 
hood of 10 to 15 per cent, of the cost of the project. 

If based on the engine horsepower, the incidentals reported by one 
consulting engineer run about as follows: 



Cost of Incidentals per Engine Horsepower 



Simple non-condensing: 

Engine horsepower 

Incidentals, cost per horsepower 

Engine horsepower 

Incidentals, cost per horsepower 

Simple condensing: 

Engine horsepower 

Incidentals, cost per horsepower 

Engine horsepower 

Incidentals, cost per horsepower 

Compound condensing: 

Engine horsepower 

Incidentals, cost per horsepower 

Engine horsepower 

Incidentals, cost per horsepower 



10 
$20 . 00 



30 
$11.00 



10 
$18.00 



40 

$10.80 



100 
$9.70 



700 

$5.75 



12 
$18.00 



40 

$9.80 



12 
$17.60 



50 
$10.30 



200 

$8.00 



800 
$5.50 



14 

$16.00 



50 

$8.30 



14 
$17.00 



75 
$8.70 



300 

$6.80 



900 

$5.25 



15 
$15.00 



75 

$6.00 



15 
$16.60 



100 

$7.80 



400 
$6.50 



1,000 
$5.00 



20 
$13.70 



20 
$14.70 



500 
$6.25 



1,500 

$4.75 



30 
$11.80 



600 
$6.00 



2,000 
$4.60 



Cost of Installations Complete. — An idea of the approximate cost of 
complete installations may be had from the following table. 



THE STEAM POWER PLANT 



249 




250 



ENGINEERING OF POWER PLANTS 



Approximate Cost per Kilowatt of Steam Turbine-driven Installations 





Size of plants — kilowatts 




5,000 


10,000 


20,000 


30,000 


40,000 


50,000 


Building, real estate and excavating 

Turbines and generators. . . . 


$17.50 
28.25 
6.85 
34.50 
5.75 
1.20 
1.90 
4.20 
2.50 
1.30 
8.50 
1.80 
5.75 


$14.60 
23.50 
,5.70 
28.70 
4.80 
1.00 
1.60 
3.50 
2.10 
1.10 
7.10 
1.50 
4.80 


$13.10 
21.20 
5.15 
25.80 
4.30 
0.90 
1.45 
3.15 
1.90 
1.00 
6.40 
1.35 
4.30 


$11.65 
18.75 
4.50 
23.00 
3.85 
0.80 
1.30 
2.80 
1.70 
0.90 
5.70 
1.20 
3.85 


$10.95 
17.65 
4.30 
21.50 
3.60 
0.75 
1.20 
2.60 
1.60 
0.85 
5.30 
1.10 
3.60 


$10.20 
16 50 


Condensers 


4.00 


Boilers, stokers, superheaters and stacks . . . 

Bunkers, and conveyors 

Boiler feed and service pumps 

Feed- water heaters 


20.00 
3.40 
0.70 
1.10 


Switchboard and wiring 


2.50 
1.50 




0.75 




5.00 


Crane 


1 00 


Supt. and engineering, etc. 


3.35 








$120.00 


$100.00 


$90.00 


$80.00 


$75.00 


$70.00 



Averaging the figures above shows the percentage distribution of cost 
to be approximately: 

Per cent, of 
total cost 

Building, real esta.te and excavating 14 . 6 

Turbines and generators 23 . 5 

Condensers 5.7 

Boiler-s, stokers, superheaters and stacks 28 . 7 

Bunkers and conveyors 4.8 

Boiler feed and service pumps 1.0 

Feed-water heaters 1.6 

Switchboard and wiring 3.5 

Exciters 2.1 

Foundation (machinery) 1.1 

Piping and conduits 7.1 

Crane 1.5 

Supt. and engineering, etc 4.8 



100.00 



Comparative Cost of Steam Power Stations, Complete. — The follow- 
ing values will illustrate the relative cost of different types of power 
stations. The figures are for complete plants including engines, genera- 
tors, boilers, piping, feed pumps and heaters, stacks and buildings. 
Direct-connected generators — one reserve unit. 



THE STEAM POWER PLANT 

Cost of Steam Power Stations 



251 



Horsepower 



100 



200 



400 



600 



1,200 2,000 



Simple non-condensing high-speed 

Compound non-condensing high-speed. 

Compound condensing 

DeLaval turbine 

Vertical condensing low-speed 

Horizontal condensing low-speed 

Parsons turbine 



$12,960 
14,140 
15,230 
14,860 



$19,280 
21,180 
22,740 
21,180 



$32,210 
34,370 
37,400 
36,050 
52,280 
51,420 



$43,950 
45,940 
49,890 
48,300 
69,470 
69,490 
60,060 



$78,300 
79,860 
85,990 
84,240 
108,990 
102,500 
88,090 



155,930 
148,310 
122,100 



Cost per Kilowatt of Several Stations 



Electric Ry. Econ- 
omy, 1903, Mc- 
Graw Pub. Co. 



Max. 



Min. 



Yorkshire 
Power Co., 
6,000 kw. 
Thornhill 



10,000- 

kw. 
engine 
plant 



90,000- 

kw. 

turbine 

plant 



150,000- 

kw. 

plant 

(London) 



Green- 
wich 
London, 

34,000 
kw. 



Land 

Foundations. 

Buildings 

Stacks 

Total building 

Boilers 

Superheaters 

Stokers 

Economizers 

Coal and ash 

Piping 

Heaters and pumps. 

Prime movers 

Condensers. 

Crane 

Exciters 

Switchboard cables. 

Incidentals 

Total equipment. . . 
Total 



$3.50 
15.00 
2.00 
20.50 
17.00 



3.00 
4.50 
7.50 

12.00 
3.00 

53.00 



10.00 

2.00 

112.00 

132.50 



$1.50 
8.00 
1.00 

10.50 
9.00 

2.50 
2.50 
3.00 
4.00 
2.00 
38.00 



4.50 

2.00 

67.50 

78.00 



$0.43 



13.4 



78.00 
91.40 



$1.22 

9.70 

1.22 

12.14 

12.10 

2.42 
1.46 
1.94 
7.30 
0.97 
58.30 
6.30 

1.46 
2.42 

94.67 
106.81 



$2.14 
4.17 



17.80 



10.55 



2.67 



37.33 



$1.60 
14.50 
16.10 

6.45 

1.94 
3.40 

13.85 

2.13 

27.77 
43.87 



$56.55 

14.69 

1.56 
7.86 

28.40 
1.07 

5.12 

58.70 
115.25 



Stevens and Hobakt. Snell, 1912. Rider, I. E. E., 1909. 

Operating Expenses. — Before deciding on the best and most eco- 
nomical plant for a given set of conditions, it is necessary to consider the 
relative yearly expense. This may be divided into fixed charges which 
are a function of the cost of the plant and must be paid whether or not 
power is produced; and operating cost or as it is often termed, station 
cost. The original division by Hopkinson in 1892 was into two similar 
categories: (a) a fixed charge depending on the maximum rate at which 
the energy may be demanded and independent of the time over which 
the demand may extend; and (6) a running charge proportional to the 
time the demand is kept up. His fixed charge might be termed a '^ readi- 
ness to serve charge" and included interest on cost, taxes, insurance, 
amortization plus the expense for labor, fuel, stores, etc., needed to keep 



252 



ENGINEERING OF POWER PLANTS 



the plant running light and ready to work. His running charge^ included 
the additional fuel, labor, repairs, and stores necessary for the carrying 
of the load. 

Hopkinson's categories proved to be subject to disadvantages due to 
the difficulty of segregating ''light running charges" from the other run- 
ning charges but the substantial accuracy of the method has never been 



Baromefnc 
Condenser- 



20.000 Kw. Turbine 



^^mhm& 



35.000 Sq. Ft. 
Condenser. {52J500 
Jffl Ft now instal- 
led) 




1000 Kw House'' 
AlfernatoriTurbine 
Driven) 



Hot Well Pump 




5iorage \\ Tank 



■Surge Pum^ 



Fig. 165. — Diagram of auxiliary connections Conners Creek Station, Detroit 

Edison Co. 



denied. He gave figures for a 2,500-kw. plant in which the ''running 
light" charges amounted to $136,000 and the fully loaded charges to 
$288,000. The "light running" charge per kilowatt of demand is not 
far from $54.30 and the corresponding costs of production including 
standing and running charges for the various use factors are given in the 
following table. 



Per cent, use factor 


Cost, cents 


Per cent, use factor 


Cost, cents 


5 


12.72 


55 


1.74 


10 


6.68 


60 


1.66 


15 


4.66 


65 


1.58 


20 


3.66 


70 


1.52 


25 


3.06 


75 , • 


1.46 


30 


2.66 


80 


1.40 


35 


2.38 


85 


1.36 


40 


2.16 


90 


1.32 


45 


1.98 


95 


1.28 


50 


1.86 


100 


1.26 



1 A very good account of the discussion of these principles may be found in Word- 
ingham's ''Central Electrical Stations" and in the Transactions of the Institute of 
Electrical Engineers (London, Eng.), 



THE STEAM POWER PLANT 253 

The later and present practice is to include interest, depreciation, 
taxes and insurance in fixed charges and fuel, labor, including superin- 
tendence, water, oil, waste and supplies, and maintenance in station cost 
or operating cost. The sum of the two is called total cost or better, 
production cost. 

These may be tabulate as follows: 

Fixed Charges: 

(a) Interest on investment. 

(6) Depreciation (replacement). 

(c) Taxes, (city, state, etc.). 

(d) Insurance. 

Station Charges: 

(a) Fuel. 

(b) Labor (including superintendence). 

(c) Oil, waste and supplies. 
id) Water. 

(e) Maintenance. 

Interest. — It is usually fair to allow 6 per cent, for interest on invest- 
ment but small industrial plants usually have to pay higher rates, say 
7 or 8 per cent. Municipalities may pay as low as 4 per cent, and it has 
been possible in Europe in the past to figure on a smaller return. For the 
general run of problems it is safe to use 6 per cent. 

Depreciation. — Structures and machinery grow old and unfit for the 
purpose for which they were erected or purchased. They may be kept 
in reasonable repair by the ordinary running maintenance but there will 
come a time when the plant is worn out and must be replaced if the busi- 
ness is to continue. If the business ends with the life of the plant, as in 
some mining propositions, the capital has been destroyed and the investor 
only gets the interest return which in this particular case must be high. 
To meet the above conditions, it has grown to be the custom to set aside 
every year a sum of money which is known by various names, depending 
on how it enters into the accounts, such as sinking fund, depreciation or 
amortization. It may be paid to the stockholders either as extra divi- 
dends or by putting it into improving the value of the plant and these 
two ways are considered the best methods for private business and small 
close corporations. For public corporation plants the sinking-fund 
method is the best as in these plants the capital is furnished by the .sale 
of bonds which must be redeemed at a certain time. All corporations 
other than close corporations should use the depreciation method and 
invest the depreciation fund so that when the old plant wears out or is 
superseded the money will be available to build a new one. 

The very rapid development of the power generation and distribution 
business in the last 30 years has shown the difference between the actual 



254 ENGINEERING OF POWER PLANTS 

life of power-generating machinery and its useful life; or its life up to the 
time that its use is superseded by larger and more economical apparatus 
or a machine better suited to changed conditions of power generation. 
The following table shows the actual life which has been' estimated for 
various portions of steam power-plant equipment. 

Appeoximate Useful Life of Various Portions of Steam Pov/er-plant 

Equipment 

Years 

Buildings, brick or concrete 50 

Buildings, wooden or sheet-iron 15 

Chimneys, brick 50 

Chimneys, self-sustaining steel 25 to 40 

Chimneys, guyed sheet-iron 5 to 10 

Boilers, water-tube 30 to 50 

Boilers, fire-tube 15 

Engines, slow-speed " ' 25 

Engines, high-speed 15 

Turbines 10 to 20 

Generators, direct-current 5 to 20 

Generators, alternating-current 5 to 20 

Motors 10 to 20 

Pumps . 25 

Condensers, jet 10 to 20 

Condensers, surface 10 to 20 

Heaters, open 30 

Heaters, closed 20 

Economizers 5 to 10 

Wiring . . 20 

Belts.. 7 

Coal conveyor, bucket 5 to 10 

Coal conveyor, belt 2 to 5 

Transformers, stationary 30 

Rotary converters 25 

Storage batteries 3 to 5 

Piping, ordinary 12 

Piping, first-class 20 to 30 

So much depends upon the design and the conditions of operation 
that no fixed values can be definitely assigned and the above figures 
should be used with caution. Practice shows that most power-plant 
appliances become obsolete long before the limit of their useful life is 
reached. 

The Traction Valuation Commission in Chicago in 1906 gave the 
following percentages for plant depreciation: 

Per cent. 

Engines, CorlissJ low-speed 3 to 5 

Engines, automatic, high-speed 5 to 10 

Cable-winding machinery 3 



THE STEAM POWER PLANT 255 

Per cent. 

Generators, direct-connected, modern ■ 5 

Generators, belted (depending on date) 5 to 10 

Traveling cranes 2 

Switchboard and all wiring 2 

Piping 35 

Pumps 5 

Heaters, closed 6 to 10 

Heaters, open, if cast iron only 3 

Breeching and connections, brick 5 

Breeching and connections, steel 10 

Boilers and settings, horizontal tubular 10 

Boilers and settings, water-tube 3.5 

Grates 10 

Coal-handling machinery 6 

Ash-handling machinery 8 

Combined coal- and ash-handling machinery 7 

Storage bins, steel 3 to 10 

Miscellaneous items 5 

''The above annual rates of depreciation have been used as a basis in 
depreciating the power-plant equipment. Apparatus has been depreci- 
ated at these rates down to 20 per cent, of the wearing value, the wearing 
value being determined by subtracting the scrap value from the cost new. 
All power-plant equipment has been considered as worth 20 per cent, of 
its wearing value as long as it is in operatin'g condition. Depreciation 
is applied to wearing value, as the apparatus is always worth scrap value. ^' 

The above percentages applied to a particular plant of 2,900-kw. 
capacity give an approximate depreciation for the whole plant of 4 per 
cent. 

It is idle to attempt to figure actual depreciation on a power plant 
from the above figures as many extraneous conditions enter into the prob- 
lem. The difference between good and bad feed water might vary the 
10 per cent, allowed for boilers from 4 to 20 per cent. 

For a well-maintained plant the allowance might be only about one- 
half as much for depreciation as for one poorly maintained. For design 
and comparison purposes it is best to assume a fixed percentage for de- 
preciation. It is customary to use 6 per cent, and the error from the 
use of this figure is not likely to be large in the present state of the art. 

Taxes and Insurance. — Taxes will vary from 1 to 2 per cent, of the 
value of the property. Insurance of buildings and machinery will vary 
from 0.5 to 1.5 per cent. These two items are usually combined for 
estimating purposes at 2 per cent. 

TOTAL FIXED CHARGES. 

Fixed charges for estimating purposes may then be taken as: 
Interest, 6 per cent. 



256 ENGINEERING OF POWER PLANTS 

Depreciation, 6 per cent. 

Insurance and taxes 2 per cent. 

Total, 14 per cent. 

This value may be used in estimates and for solving the problems in 
these notes. 

This total allowance of 14 per cent, for fixed charges may be regarded 
as fair when the operating portions of such installations are alone con- 
sidered. 

When the buildings of brick or concrete make up a large proportion 
of the investment, an average of 11 per cent, for fixed charges is perhaps 
a better figure. 

STATION COST 

Fuel. — The available fuels for power-station purposes are the steam 
sizes of anthracite coal, bituminous coal, oil and natural gas. The steam 
sizes of anthracite include all the finer grades from pea coal down to 
the refuse or culm. Culm which may contain as high as 35 per cent, ash 
costs about 25 cts. a ton at the mine. No. 3 buckwheat or rice coal about 
50 cts., No. 1 buckwheat about 80 cts. and pea coal about $1. Bitumin- 
ous coal, which varies greatly in quality, also varies much in price at 
the mines averaging from 90 cts. to $1.50 per ton. The average freight 
rate on coal is 13^^ cts. per ton-mile. 

Anthracite coal is used in the anthracite regions and to a consider- 
able extent in the regions round about extending to New York and Phila- 
delphia,, but the steam fuel of the whole country as a rule is bituminous 
coal. The price at the power station will vary from $12 in certain unac- 
cessible localities down to 90 cts. near the mines. 

Oil, usually the crude oil of commerce, varies in price per barrel of 
42 gal. at the well from 40 to 60 cts. 

Oil is handled by pipe lines in the regions near the wells but a good deal 
of it is water-borne and the freight is relatively much lower than for coal. 
Contracts for Mexican and Texas oil have been offered in New York and 
Philadelphia for $1.25 per barrel. 

Oil will probably be an available fuel only in the Pacific States where 
coal is high and poor and in Texas and Oklahoma. 

At a distance from the wells the price usually runs from 2 to 4 cts. 
per gallon. 

Although natural gas is found in limited quantities in many sections 
of the United States, its use for power-plant purposes is largely in the 
region of Pennsylvania, Ohio and West Virginia. The gas is piped from 
the wells and costs from 10 to 30 cts. per 1,000 cu. ft. 

The cost of fuel must always be ascertained for the particular locality 
as large variations in price occur in an unexpected way due to local condi- 



THE STEAM POWER PLANT 



257 



tions. Before the discovery of the Cahfornian oil fields most of the steam 
fuel used in San Francisco was Welsh coal brought out as ballast or to 
help make up a cargo. For the same reason Canadian coal was largely 
used in Westphalia, Germany, before the outbreak of the European war. 



Control Koom 




SCALE OF FEET 
10 20 30 40 50 60 70 80 90 100 



Fig. 166.— Carville Power Station, Wallsend on Tyne. 



The price of the coal is not the only fuel cost. The coal must be put 
into the station bunkers, the ashes must be removed and disposed of and 
these costs should be added to the cost of coal. If the coal is insured, 
this cost is fuel cost and if stored for any time the interest cost should be 
added. 



258 



ENGINEERING OF POWER PLANTS 




THE STEAM POWER PLANT 



259 



For known conditions the fuel consumption should be determined by 
using the B.t.u. value of the fuel and a proper boiler and furnace efficiency. 

Some idea of the average coal consumption of plants of different sizes 
may be obtained from the following table, based on the coal per horse- 
power-hour. 

Coal per Horsepower per Hour 



Simple non-condensing: 

Engine horsepower 

Total coal, pounds 

Engine horsepower 

Total coal, pounds 

Simple condensing: 

Engine horsepower 

Coal, running times, pounds. 
Total coal, pounds 

Engine horsepower 

Coal, running times, pounds 
Total coal, pounds 

Compound condensing: 

Engine horsepower 

Coal, running times, pounds. 
Total coal, pounds 

Engine horsepower 

Coal, running times, pounds. 
Total coal, pounds 



2 
13.0 



14 
7.0 



10 
6.1 
7.0 

30 

4.60 
5.25 



100 

2.75 

3.15 

800 

2.15 

2.50 



3 
10.5 



15 
6.5 



12 
5.9 
6.75 

40 
4.20 
4.75 



200 
2.45 

2.85 

900 
2.10 

2.45 



8.5 



14 
5.7 
6.50 

50 
3.75 
4.25 



300 

2.40 

2.75 

1,000 
1.95 
2.25 



30 
5.5 



15 
5.25 
6.00 

75 
3.40 
3.70 



400 

2.35 

2.70 

1,500 
1.80 
2.05 



7.6 



40 
4.75 



20 
4.80 
5.50 

100 

3.10 

3.50 



500 

2.30 

2.65 

2,000 
1.75 
2.00 



10 
7.4 



50 
4.5 



600 

2.25 

2.60 



12 
7.25 



75 
4.0 



700 

2.20 

2.55 



Kent states^ that small engines and engines with fluctuating loads are 
usually very wasteful of fuel. The following figures, illustrating their 
low economy, are given by Professor Unwin, Cassier^s Magazine, 1894. 

Small Engines in Workshops in Birmingham, England 



Probable i.hp. at full load 

Average i.hp. during observation 

Coal per i.hp. per hour during observa- 
tion, pounds 



12 
2.96 

36.0 



45 
7.37 

21.25 



60 

8.2 

22.61 



45 
8.6 

18.13 



75 
23.64 

11.68 



60 
19.08 

9.35 



60 
20.08 

8.50 



It is largely to replace such engines as the above that power will be 
distributed from central stations. 

Labor. — This charge should include the wages of all stokers, oilers, 
engineers, laboratory men, switchboard operators, electricians, clerks, 
janitors, watchmen and such portion of superintendence as is given to 
the station. 

The wages of all men employed on repairs should be charged to 
maintenance. 

1 "Mechanical Engineers* Pocket-book," p. 964. 



260 



ENGINEERING OF POWER PLANTS 







xduuYJduiJojsuojj_ 



THE STEAM POWER PLANT 



261 



The cost of attendance will depend upon the size of the plant, in gen- 
eral, being less for a large plant, i. e., relatively less. 

The salaries paid engineers vary from $60 per month to $150 for ordi- 
nary plants. 

Firemen receive from $50 to $90 per month, the average being about 
$65 for 12-hr. days. 

Coal passers and ash wheelers receive about $30 to $55 per month. 

In New York and Philadelphia firemen and coal passers receive in the 
neighborhood of $2 to $2.25 per 8-hr. day. 

In general the yearly (3,080) hours cost of attendance will run about: 



For simple non-condensing plants: 

Engine horsepower 

Attendance 

Engine horsepower 

Attendance 

For simple condensing plants: 

Engine horsepower 

Attendance 

Engine horsepower 

Attendance 



2 
$99 


3 

$109 


4 
$116 


6 
$136 


8 
$154 


10 
$173 


12 
$184 


15 
$202 


20 
$230 


30 

$287 


40 
$338 


50 
$390 


75 
$520 




10 

$178 


12 
$190 


14 

$202 


15 
$210 


20 
$238 


30 
$297 




40 

$350 


50 

$405 


75 
$535 


100 
$670 









14 
$194 



One man attends engine, fires boiler and is supposed to do other work 
besides. On the 10-hp. plant one-half of his time is charged to attend- 
ance and three-fourths of his time on the 100-hp. plant. 



For compound condensing plants 

Engine horsepower 

Number of men and wages 

Total attendance 

Engine horsepower 

.Number of men and wages 

Total attendance 



100 
1 at $16 



$800 

700 

1 at $17 

2 at $22 
1 at $10 

$2,650 



200 
1 at $16 
1 at $7 



$1,220 

800 

1 at $18 

2 at $22 
1 at $10 

$2,700 



300 
1 at $16 

1 at $7 



$1,220 

900 

1 at $18 

2 at $25 
1 at $10 

$2,930 



400 
1 at $16 
1 at $10 
1 at $7 

$1,760 

1,000 

1 at $19 

2 at $26 
2 at $20 

$3,480 



500 
1 at $16 
1 at $13 

1 at $7 

$1,930 

1,500 

1 at $22 
3 at $36 

2 at $20 

$4,400 



600 
1 at $17 
1 at $13 
1 at $10 

$2,100 

2,000 

1 at $25 
4 at $50 

2 at $20 

$5,200 



These costs are below the average for the larger sized plants. 

Better labor costs per year are given by the following formulas. 

For plants from 400 to 1,000 i.hp. 

Cost in dollars = 1,500 + 3 X hp. 
For plants from 1,000 to 5,000 i.hp. 

Cost in dollars = 2,000 + 2 X hp. 



262 



ENGINEERING OF POWER PLANTS 



In a large electric steam-turbine central station the v/ages involved 
in the cost of power delivered by one unit (14,000-kw. Curtis turbine, 
8 B. & W., boilers of 5,000 sq. ft. of heating surface each and auxiliaries) 
to the switchboard are: 

General Engineering Force: 

Cost per day 

One chief engineer at $250 per month, }4 of his time $1 . 40 

One assistant chief engineer at $200 per month, 3^ of his time 1.11 

One chief electrician at $200 per month }i of his time 1.11 

One assistant chief electrician at $150 per month, ^ of his time. ... 0.83 

Three load despatchers at $100 per month, 3^ of their time 1 . 66 

One boiler-room foreman at $100 per month, % of his time 0.55 

Operators for One Generating Unit: 

Three watch engineers at $4 per day of 8 hr $12 . 00 

Three oilers at $2.50 per day of 8 hr 7. 50 

Three switchboard attendants at $2.50 per day of 8 hr. ; 7. 50 

Three firemen at $2.50 per day of 8 hr 7 . 50 

Three water tenders at $2.50 per day 7 . 50 

One boiler washer at $2.50 per day of 8 hr 2 . 50 

One pipe fitter at $3 per day of 8 hr. 3 . 00 

One pipe fitter helper at $1.50 per day of 8 hr 1 . 50 

Four laborers at $2 for coal handling 8 . 00 

Total $63 . 66 

Herrick has given a table of interest in connection with the labor item. 



Plant 


Rating, 
kw. 


Output, 
kw.-hr. 


Total station 
wages 


Labor per 

kw.-hr., 

cents 


Total station 

cost, kw.-hr., 

cents 


Number of 

station 
employees 


A 


6,000 


8,776,165 


$25,937 


0.296 


1.21 


22 


B 


5,000 


6,043,204 


20,920 


0.346 


1.23 


20 


C 


4,000 


5,400,192 


19,429 


0.360 


1.24 


28 


D 


2,000 


3,288,623 


9,954 


0.302 


1.42 


11 


E 


2,000 


4,305,003 


9,663 


0.224 


1.27 


13 


F 


1,250 


1,470,066 


6,844 


0.465 


1.56 


8 


G 


950 


1,479,898 


8,771 


0.595 


2.05 


7 


H 


700 


889,760 


6,669 


0.750 


2.34 


8 


I 


630 


730,458 


5,017 


0.685 


1.80 


6 



ant 


Kw. per station 
employee 


Wages per kw. 
station capacitji 


A 


272.0 


$4.31 


B 


250.0 


4.18 


C 


136.0 


5.10 


D 


182.0 


4.97 


E 


154.0 


4.83 


F 


157.0 


5.45 


G 


136.0 


9.25 


H 


87.5 


9.52 


I 


105.0 


7.95 



THE STEAM POWER PLANT 



263 



Maintenance. — This is the cost of maintaining the building and ma- 
chinery in good working order and includes both materials and labor, the 
object being to have the plant in 
as good condition as a going concern 
as it was when built. 

There are many standards of 
good running order and an increase 
in this item usually means a de- 
crease in the fuel item. Six per 
cent, of the station charges is a fair 
average allowance for maintenance. 

Oil, Waste and Supplies. — Good 
cylinder oil in small quantities costs 
from 30 to 60 cts. per gallon. In 
quantity it may be purchased from 
25 to 40 cts. Bearing oil is cheaper 
and runs from 18 to 30 cts. Good 
bearing oil in quantity should cost 
from 23 to 27 cts. a gallon. 

The amount of oil required 
varies greatly with the type of in- 
stallation, the periods of continuous 
service and the care of the engine 
operator. So great is this varia- 
tion that average figures mean little, [ 
but they will serve in making esti- 
mates of operation costs. A com- 
parison of many returns shows 
the amount of cylinder oil and 
the amount of engine oil used to 
be practically equal for reciprocat- 
ing steam engines. 

The average returns from a 
number of installations show the 
consumption of each kind of oil to 
be approximately 1 pt. per 1,000 
hp.-hr. or 1 pt. per 1,000,000 sq. ft. 
rubbed over. 

Turbines require no cylinder 
oil and use bearing oil only. As 
each unit has its oil system only 
the make-up and auxiliary oil have 
to be considered. It has been the 




264 



ENGINEERING OF POWER PLANTS 



custom of some oil companies to contract to furnish all the oil needed 
at a certain price per kilowatt-hour generated. The prices have varied 
between 0.01 and 0.02 ct. per kilowatt-hour. 

White waste of good grade may be purchased in 150-lb. bales at about 
9 cts. per pound (variation 7 to 11 cts.). This item may amount to con- 
siderable unless care is taken. 

Relatively large financial savings may be made by using a waste and 
oil separator. By this means waste may be used six or eight times and 
large amounts of oil are recovered which, after filtering, may be reused. 

One small station of about 750- or 1,000-hp. capacity installed such 
a separator at a cost of $150, and saved $90 in oil and waste the first 
month. The- average saving per month in this plant is over $100. 

In the larger stations washable cheesecloth towels have replaced waste. 

Supplies include such small articles as packings, small pipes, valves 
and fittings, tools, wrenches, gaskets and other small articles which must 
be kept in stock. They should include laboratory supplies, stationery, 
janitors' supplies, and other items of this kind. 

These three items are usually lumped together and form a small part 
of the station cost in a large plant. 

One consulting engineer reports the yearly (3,080 hr.) cost of oil, 
waste and supplies to run approximately as follows: 



Simple non-condensing: 

Engine horsepower 

Oil, etc 



Engine horsepower. 
Oil, etc 



Simple condensing: 
Engine horsepower. 
Oil, etc 



Engine horsepower. 
Oil, etc 



Compound condensing: 
Engine horsepower. . . . 
Oil. etc 



Engine horsepower. 
Oil, etc 



2 

$13.20 



15 
$26.50 



10 
$22.80 



40 
$53.00 



100 
$143.00 



800 
$420.00 



3 

$14.30 



20 
$31.20 



12 
$24.80 



50 
$64.00 



200 
$205.00 



900 
$445.00 



4 
$14.30 



30 

$41 . 50 



14 

$26.70 

75 
$89.00 



300 
$240.00 



1,000 
$470.00 



$17.60 



40 
$51.00 



15 

$27 . 60 

100 
$114.00 



400 
$285.00 



1,500 
$600.00 



$20.00 



50 
$61 . 50 



20 

$32 . 50 



500 
$315.00 



2,000 

$685.00 



10 
$22.00 



75 
$85 . 50 



30 
$43.00 



600 
$350.00 



12 

$23 . 80 



700 
$385.00 



14 

$25. S 



These costs are below the average for the larger size plants. 

Water.^-This expense will be relatively small with a condensing sta- 
tion even where city water is used. In many cities the cost of water for 
manufacturing purposes is 40 cts. per 1,000 cu. ft. or 5.35 cts. per 1,000 gal. 
For New York City the price is $1 per 1,000 cu. ft. Where fresh water 
is used for condensation the feed water can usually be taken from the 



THE STEAM POWER PLANT 265 

tail pipe and will cost nothing. With turbine stations and surface con- 
densers the make-up is very small and the water item is smaller than the 
oil item. Caution should be exercised in using Artesian or other well 
water as feed water if its chemical composition is not known. 

PROBLEMS 

65. Estimate the cost of a small power plant of 125 i.hp. The estimate is to be 
based on the assumption that the engine and boiler are not more than 20 ft. apart; 
that water supply is brought into the engine room by customer; that exhaust valve 
and safety-valve exhaust are to be carried outside of the engine room a distance of not 
more than 20 ft.; that sewer connection is made in engine room to which drip pipes 
and blowoff pipes may be carried 

1. 125-hp. simple non-condensing engine, on cars. 

2. Freight to destination, estimated. 

3. Cartage and handling to position, about $5 per ton. 

4. Foundation. 

5. Boiler, horizontal fire-tube, horsepower. 

6. Freight. 

7. Handling, 

8. Setting. 

9. Iron stack. 

10. Erecting. 

11. Two feed pumps. 

12. Feed-water heater. 

13. Pipe connections, steam, exhaust and water pipe. 

14. Pipe covering for all steam pipe. 

15. Man to superintend erection (customer furnishing all laboring help in handling 
heavy pieces) 5 days at $5 per day. 

16. Railroad expenses from factory and board. 

17. Add to above for contingencies, 5 to 10 per cent. 

18. Add consulting engineer's or agent's commission, if any. 

19. Add expense of test after erection, if required. 

66. An equipment is to be selected for a steam power plant capable of developing 
750 hp. Three estimates are to be made as follows : 

A. Two 300-hp. compound, high-speed, non-condensing engines and one 150-hp. 
compound, high-speed, non-condensing engine. Return tubular boilers. Equal 
units. Two in operation, and one in reserve. Flat grates, hand-fired. Equivalent 
evaporation 7.5 lb. water per pound of coal. 

B. Two 300-hp. compound, condensing Corliss engines and one 150-hp. compound, 
condensing high-speed engine. Water-tube boilers and mechanical stokers. Same 
arrangement of boilers as in ''A." Equivalent evaporation 8 lb. water per pound coal. 

C. Two 375-hp. compound, condensing Corliss engines. Boiler equipment and 
conditions as in "B." 

Determine the best plant to install : 

(a) If water is purchased and wasted to sewer. 
(6) If water costs nothing but pumpage. 

Note. — Standby losses need not be considered in this problem. 



266 ENGINEERING OF POWER PLANTS 

Investment "A." 

1. Two 300-hp. engines, erected .........$ 

2. Foundations for two engines 

3. One 150-hp. engine, erected 

4. Foundation for engine 

5. boilers, hp. each, including setting 

6. Brick stack 

7. Flues 

8. Two feed pumps 

9. Two feed-water heaters 

10. Piping 

11. Boiler house 

12. Engine house 

13. Coal pocket 

14. Incidentals 

Total $ 

Investment "B." 

1. Two 300-hp. engines and condensers, erected 

2. Foundations for two units 

3. One 150-hp. engine and condenser, erected 

4. Foundation 

5. boilers, hp. each, including setting 

6. Brick stack 

7. Fhies 

8. mechanical stokers 

9. Two feed pumps 

10. Two feed-water heaters 

11. Piping 

12. Boiler house. 

13. Engine house 

14. Coal pocket 

15. Incidentals 

Total $ 

Investment "C." 

1. Two 375-hp. engines and condensers, erected 

2. Foundations for two units 

3. boilers, hp. each, including setting 

4. Brick stack 

5. Flues 

6. mechanical stokers 

7. Two feed pumps 

8. Two feed-water heaters 

9. Piping 

10. Boiler house 

11. Engine house 

12. Coal pocket 

13. Incidentals 

Total $ 



THE STEAM POWER PLANT 267 

Estimated Operating Cost. — Service 10 hr. per day, 308 days per year. Load on 
engine = 85 per cent, of full-load rating. 

Plant "A" 

Amount $ per 

per day day 

1. Coal: Tons for two 300-hp. engines 

Tons for one 150-hp. engine 

Tons for auxiliaries and leakage 

2. Attendance: engineers at $ 

firemen at $ 

coal passers at $ 

3. Oil : Cylinder oil for all engines 

Engine oil for all engines 

4. Waste and supplies 

5. Water : M cu. ft. for two 300-lip. engines 

M cu. ft. for one 150-lip. engine 

M cu. ft. for auxiliaries and leakage 

6. Maintenance, 6 per cent, on $ 

Operating expenses only $ 

7. Fixed charges at per cent, on $ 

Total operating cost and fixed charges $ 



Plant ''B" 

Amount $ per 

per day day 

1. Coal: Tons for two 300-hp. engines . 

Tons for one 150-hp. engine 

Tons for auxiliaries and leakage. 

2. Attendance: engineers at $ 

firemen at $ 

coal passers at $ 

3. Oil: Cylinder oil 

Engine oil 

4. Waste and supplies 

5. Water: M cu. ft. for auxiliaries and leakage 

M cu. ft. for circulating water 

6. Maintenance, 6 per cent, on $ 



Operating expenses only $ 

7. Fixed charges at per cent, on $ • 

Total operating cost and fixed charges % 

Plant ''C" . 

. Amount $ per 

per day day 

1 . Coal: Tons for two 375-hp. engines. 

Tons for auxiharies and leakage 

2 . Attendance: engineer at $ 

firemen at $ 

coal passers at $- 

3. Oil: Cylinder oil 

Engine oil , 



268 ENGINEERING OF POWER PLANTS 

4. Waste and supplies 

5. Water : M cu. ft. for auxiliaries and leakage 

M cu. ft. for circulating water 

6. Maintenance, 6 per cent, on $ 

Operating expenses only $ 

7. Fixed charges at per cent, on $ , 

Total operating cost and fixed charges 

Summary 

ABC 

Investment 

Excess cost over "A" 

Total operating cost per year 

Saving in operation cost per year over "A" 

Time to make up difference in first cost by saving in 

operating expenses 

Total indicated horsepower-hours 

Cost per indicated horsepower-hour , . 

67. Assuming the same types for the installation as in problem 66 estimate 
the operating cost for 24 hr. service for 365 days per year. 

68. It is proposed to install a power plant consisting of two 1,000 i.hp. Corliss 
compound condensing engines; six 300 hp. water-tube boilers, with chain grates, etc.; 
and the necessary electrical equipment. The entire plant, exclusive of buildings, 
costs, erected, $140,000. The plant is to be located on the shore of a lake so that 
the water costs nothing. It is to operate at 70 per cent, engine rating for 10 hr. per 
day and at 45 per cent, rating on one engine for 14 hr. per day for 365 days per year. 
About the time the contract is to be let, an electric company offers to furnish the power 
required for a flat rate of $85,000 per year. Will it pay to put in the plant or would 
it be better to accept the offer of the electric company? Show figures and state 
reasons. 

Note. — Stand-bv losses need not be considered. 



CHAPTER XIII 
VARIABLE LOAD ECONOMY 

The making of power, up to a very few years ago, was entirely a local 
business, each mill, shop or factory was located at the power supply, or 
when steam was used the engine was located in or near the factory build- 
ing. The transmission to the machines was by shafting, gears or belts. 
About 60 years ago rope transmission and a little later hydraulic and 
compressed-air transmissions were introduced in certain localities in 
order that the power might be used at some distance from the point of 
generation. About 30 years ago electrical transmission came into use 




Fig. 170. — Jumbo dynamo and Armington & Sims engine. 
Station unit, built June, 18S-1. 



The first Central 



and with it the central station became an established fact. Both the 
hydraulic transmission, so well applied at London and Geneva, and the 
compressed-air transmission, as it was used in Paris, might have been 
capable of development, but the essential convenience and economy of 
the electrical transmission and drive soon gave it first place, and today 
when one speaks of the central-station supply of power the electrical 
system is implied. 

The electrical transmission of power has its disadvantages, the chief 
being the impossibility of storing power in any quantity. Electricity 

269 



270 



ENGINEERING OF POWER PLANTS 



must be used as generated. This means that there will be a varying load 
on the central station at all times and that the generators must be large 
enough to generate the maximum power required at one time and also 
must be run at something below the best efficiency most of the time. 
This variation of load is best shown by a load curve, plotted with time 



25U 


Uaz. Load 20 
Total CoDBun 
Load Factor 


1 Jai..l 
1 K.W. Ooeured 
ption Per Mont 
34 Per Cent 


h 51578 


.tU.. 

KW. E 


) p.a 

Irs. 


. 




125 
100 
75 
50 
25 





1 1 1 <^;an.l912 | 
Max.! Load 83 K.W. jOccuied from 3.30 tl 
Total Consumption Per Month 31460 K.V 
Load Factor 54 Per Cent | 


J.M. 
r. Hrs. 














r- 


'T. 


^1 


/^ 


















xr\_ P- 










inn 
































J 




■J 




X 


^ 


T. 












r 










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'I 


- 





^ 


^ 


-U- 


J 










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■^ 




-n. 





















6 

A.iir. 



Fig. 171. — ^Load curve of average size 
department store. 



12 2 4 6 8 10 12 2 4 6 8 10 12 
M. A.M. K. E.M. 

Fig. 172.— Load curve of U. S. Gov't. 
Post Office Building. 



for the abscissae and power for the ordinates. Such load curves for cen- 
tral stations with various kinds of load are shown in the accompanying 
figures. 

These load curves will vary from day to day and season to season, 
but for each kind of business a characteristic curve can be drawn. 





Max. 
Tota 
Loa 


— ! 

Load 85 I 

1 Consump 

Fac or 4 


J 

tlon: 
Per 


an.l9l2 
Occuied f 
>er Month 
Cen 


3007 




2 P 

7. Hi 


M. 

3. 




































/ 


Jl 


nl 


/ 


jU 








'L 


'1 




nJ 










- 


^ 


Hj- 


. 



























12 2 4 6 
M. A.M. 



10 12 2 4 6 8 10 12 
N. P.M. 



1500 
onn 




Loa 


I Factor 


J 
56.1 I 


:; 


913 

nt 




















rJ" 


f^ 


n 




















J 




P 


^ 


1, 










■^ 




r 










\ 


1 


f- 


11— 


g 




xH- 


r 












L 


/ 






12 2 


4 


6 
AM 


8 1 


1 


2 2 

I. 


4 


P. 


M. 


1 


12 



Fig. 173. — Load curve of newspaper Fig. 174. — Combined load curve of nine 
plant. large power consumers. 

Through the courtesy of The Detroit Edison Co., Figs. 166 and 167 
are presented showing the change in load distribution due to the recent 
change from central to eastern time in that city. 

One curve is plotted on clock time as a basis; the other is plotted 
on sun time. In each case the ordinates are based on the peak of the 
curve before the change of time, this peak being called lOQ per cent. 



VARIABLE LOAD ECONOMY 



271 



In comparing these curves it should be noted that the change occurred 
in the late spring and that there would naturally have been an increase 
in the depth of the valley preceding the peak, as well as a decrease in the 
height of the peak itself. 



100 



I so 

1 

VH 60 
o 



40 





/ 

/ / 
/ / 

/ / 


• ~-v 


r f 




\\ 


\ 

1 




1/ 

4/ 


V 




Y! 


\\ 
\\ 
\\ 
\ \ 


V 

V 


1 / 








\ \ 
\ 


'^>-, 


1 1 











A.M. 



12 



P.M. 



12 



Curs^es Plotted on Sun Time 
Fig. 175. — Detroit Edison Co. load curve showing effect of change of time. 



On the basis of clock time the curves show that people apparently 
lived by the clock in the morning, but that they lived more by the sun in 
the afternoon and early evening, since the peak was delayed about 1 hr. 
the exact amount by which the clocks had been moved ahead. 



100 



40 



20 





/ 


'^, 


r 




/ V 

/ V 






1 


i 


^ \j^ 


\\ 




i 








\\ 




/ 








\\ 


\ 


/ 










■^ 


/ 











' P.:M. ^ 



A.M. 
Curves Plotted on Clock Time 



12 



Fig. 176.— -Detroit Edison Co. load curve showing effect of change of time. 



This is shown in just the reverse fashion on the sun-time basis. 
Morning, noon and afternoon events are seen to be made earlier by about 
1 hr. with respect to the sun, indicating living on the basis of clock time. 
On the other hand, the peak occurs at sun time, indicating practical inde- 
pendence of the clock for the evening events. 



272 



ENGINEERING OF POWER PLANTS 



The effect of the dayhght saving schedule is perhaps more clearly 
shown by Fig. 177. 

Load Factor. — For convenience in determining operating conditions, 
the average load per day, per month or per year, is calculated, and by 
comparing this average load with the maximum load in the same time 
period, a very valuable indication of the character of the load is obtained 
The American Institute of Electrical Engineers in its standardization 



SUN TIME SCHEDULE 

Overlap OF 

LIGHT AND POWER LOAD 
p>The area shown In white atove this line re» 
reeentB the saving in capacity which would 
ave resulted by the exteneionot the daylight 
jaTing plan throueh the- winter months-'i^in 
Doth diagrams reprcBente the llghtlne load at 
t> P.M. clock time.''B"«pre3ent8 the power i 
jMd at 5 P.M. clock time"A"nluB"B"equal8 
the light load plus the power load at 5 P.M 
•-olosk ' - 



TYPICAL DAILY LOAD 



DAYLIGHT SAVING SCHEDULE 

NON-OVERLAP OF 

LIGHT AND POWER LOAD 




Fig. 177. 



rules defines ''Load Factor" as the ratio of the average load to the maxi- 
mum load during a certain period of time. The average load is taken over 
a certain interval of time, such as a day or year, and the maximum is 
taken over a short period, such as 15 min., or an hour, within that interval. 
In each case the interval of maximum load should be definitely specified. 
It is dependent upon the local conditions and the purpose for which the 
load factor is to be determined. For electric-hght plants and for oper- 
ating statistics it is usual to consider the load factor as the ratio of the 
average load for the day to the maximum 5-min. peak. In a street-rail- 
way plant where the momentary swings are larger, the period for deter- 
mining the maximum may to advantage be made as large as 30 min. or 
even 1 hr., and the maximum peak taken as the average during that 
period. The yearly load factor is the average load for the year divided 
by the maximum during the year. 



VARIABLE LOAD ECONOMY 



273 



Station economies depend on load factors to a considerable extent and 
high load factors are uncommon, except in metallurgical plants, where 
a load factor of 90 per cent, may be at times attained. Railway plants 
give load factors varying between 3 per cent, and 50 per cent. Lighting 
stations rarely exceed 30 per cent, and the smaller hghting plants are 



9000 
8000 
7000 
6000 
;5000 

I 

} 

4000 
3000 
2000 
1000 





Total [e.V 


. Hr. f 


>r r 


ay 


,46,( 


02 


j_ 














r" 


h 










-1 




"L 


J 


































































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^ 




















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T 




































r 










, 






r 


U 














, 




_i ._!_ 


Ti 
1 1 


oae 


, 


, 




, , 



7000 



5000 



^4000 



§3000 



2000 



1000 



Xdtal k. 


W. H 


r. i 


<T I^ay ^17 


,3G4 












Jl 








h 












L- 


1 




1 








±J 
















T 
























"t 
















n 






















T_ 












u 












, , 


1.. 


, 


Time 


.. L „ I 


„„1,. ,1. 



1212315678 910U12 12 3 4 5 6 7 8 910 U12 
N P.M. 



12123456789 H)U12 12 3 4 5 6 7 8 9101112 
A.M. N P.M.. 

Fig. J78.— Load curve, July 4, 1910, Fig. 179. — Typical weekday load curve. 
Aurora, Elgin & Chicago R. R. Aurora, Elgin & Chicago R. R. 




Fig. 180. — Winter load curve power and Fig. 181. — Summer load curve power 



lighting. 



and lighting. 



sometimes as low as 3 per cent. Williams and Tweedy in '' Commercial 
Engineering for Central Stations," give a list of 24 central stations with 
varying output from 900,000 kw.-hr. per year to over 32,000,000 kw.-hr. 
per year, in which the lowest load factor is 19.2, the highest load factor 
36.5, and the average for the 24 plants 28 per cent. A station with a 



274 ENGINEERING OF POWER PLANTS 

high load factor should have few units and large ones and the most 
economical apparatus will quickly pay for itself. A low load factor will 
mean smaller units and a larger number of them and the economy of at 
least half of the apparatus is of no great consequence, since it is only used 
a few hours every year. In some of the larger lighting plants as much as 
97 per cent, of the output is generated on less than 50 per cent, of the ap- 
paratus, the remaining half of the machines are in use less than 60 hr. 
out of the 8,760 hr. of the year. 

A. F. Strouse in the Electric Journal has given the following table of 
industrial load factors which may be useful: 



Per cent. Per cent. 

Boiler shops 10-20 Foundries 5-15 

Shoe factories.. 15-25 Knitting mills 25 

Breweries. 45 Machine shops 5-25 

Cement plants 60-90 Clay products 15-20 

Coal mines 15-30 Tanneries 10-20 

Cotton mills 20-30 Textiles (general) 25 

Flour mills 20-25 Woodworking shops 5-30 



Diversity Factor. — It will be noted that load factor is a measure of the 
load on the central -station system, and is independent of the type or kind 
of power generation. There is another factor which also deals with the 
system load, which is of great importance to the operator and designer. 
It has been noticed that while one piece of apparatus on an electrical 
supply main may occasionally take its maximum power, two such 
machines will not take double the power, because their maximums do not 
come at the same time. If we take the sum of the maximums of all the 
connected loads on the system and divide them by the maximum load on 
the system we have a factor which has been called the diversity factor, 
which in every case is greater than one, and in some systems may be as 
large as four or five. The National Electric Light Association, in 1912, 
changed the definition of this factor while retaining the name, as follows : 
'^ diversity factor is the ratio between the simultaneous demand of a 
number of individual services for a specified period, and the sum of the 
individual demands of those services for the same period." This defini- 
tion expressed as a fraction or as a percentage (never greater than one) 
is now universally accepted. The diversity factor of a purely lighting 
load may be as low as 25 per cent. With motor loads the factor is 50 
per cent, or higher. 

Gear {Electrical World, Nov. 10, 1910) gives the following table of 
block diversity factors and load factors for three classes of electrical 
service : 



VARIABLE LOAD ECONOMY 



275 





Analysis of Customer's 


Diversity 


Factors 






Group 


Number of 
customers 


Kw. con- 
nected per 
customer 


Sum of con- 
sumer's 
maxima 


Maximum 
of group 


Diver- 
sity- 
factor 

% 


Average 

consumers 

load 

factor 

% 


Group 
load 1 
factor 

% 




Residence Lighting 


Block A 

Block B 

Block C 

Average 


34 
185 
167 
128 


0.53 
0.53 
0.87 
0.68 


12 

68 
93 

57 


3.6 
20.0 
28.0 
17.2 


30.0, 
29.4 
30.2 
29.9 


7.0 
7.0 
7.3 
7.1 


23.3 
23.8 
24.0 
23.9 




Commercial Lighting 


Group D 

Group E 

Group F. . . . 
Group Gi... 
Average 


46 

79 

160 

221 

95 


1.28 
0.74 
0.53 
2.70 
0.70 


46 
36 
62 

403 
48 


33.0 
26.0 
41.0 
270.0 
33.0 


71.4 
71.4 
66.2 
67.5 
68.5 


13.0 
11.0 
10.0 
13.0 
10.8 


18.0 
16.0 
15.0 
19.0 
15.7 




General Motor Service 


Group H 

Group I 

Group J 

Group K 

Average 


29 
18 
11 
25 
21 


0.1 hp. 
3.3 
11.8 
6.0 

4.5 


30 kv.a. 
40 
90 
100 
65 


21 kv.a. 

25 

65 

70 

45 


70.0 
62.5 
71.9 
70.0 
69.5 


15.0 
16.0 
18.0 
21.0 
15.5 


21.0 
26.0 
28.0 
30.0 
26.0 



A and B, apartments; C, apartments and residences; D, small stores, saloons, 
restaurants; E, small stores above; F, apartments above stores, lodge halls, etc.; G, 
office building; H, I, J, K, mostly clothing manufacturers. 

* G is not included in average of group. 



Use Factor. — The designing engineer uses a factor analogous to load 
factor which is known as the use factor and sometimes as the utility fac- 
tor. This may be defined as the ratio between the average power sent 
out by the station to the maximum 24-hr. rating of the station. This 
factor is in all cases lower than the load factor by the amount of reserve. 
The load factor and diversity factor tell what part of the installation is 
used and how much it is used, but they do not show the capacity of the 
generating station. The use factor does this and may be used for design. 

Readiness to Serve. — "The readiness to serve" item plays a large 
part in station economy. If we know what the load will be 15 min. or 
}/2 br. ahead due preparations can be made with ease and certainty. 
Where this is not known machinery must be run light in anticipation of 
a load that may never come. That such loads do come at times is shown 



276 



ENGINEERING OF POWER PLANTS 



by the ''thunderstorm peaks," which may increase the load 50 per cent, 
in 5 min. 

Central Station Design. — The power-station problem, as presented to 
the designing engineer, usually takes the form of a deductive analysis, 



65.000 
60.000 - 
55,000 



2 45,000 

t 40,000 

^ 35,000 

30.000 

25,000 

20.000 





wLUicd, yA« n \. ni ,, , 


-.^^^1 + raMt^tJt 


_^A^ -^ t ^^ctni'ijtfr^ 


4^^^^^ rf- + ^ M^ 




\ Sunday and Hoi day Lokds 


\ ,— ,'' " ._ '' \ . 






Atmospheric Temperature 


^^^3Ll|v2^33aflnlA 


.^^f^^ ^^T^^ ^ "^ 


5l^ 



10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 
Days 

Fig. 182. — Boston Elevated Ry. load curve showing effect of temperature on a 

railway load. 



starting from several given conditions which are at once the basis and 
the limitation of the problem. These conditions may be scheduled as 
follows: First, method of power generation; second, the type of load, that 
is, the load factor and diversity factor; third, the locality over which the 
power is to be distributed and used; fourth, various restrictions depend- 
ing on peculiar physical, political or commercial considerations. Of these 
conditions the last two are always beyond the control of the designing 
engineer, while the first two are more or less directly under his control, 
and should be the subject of careful studies to insure the best solution. 
Under location, it is necessary to consider the territory to be covered, the 
distribution of population, lines and distribution of travel and manufac- 
turing and commercial localities. If the central station is to supply a 
lighting load, a power load, a railway load or any combination of these, 
the locality must be studied with reference to these conditions. The 
various political, commercial and artistic restrictions, under the fourth 
category, must be taken into consideration in the analysis, leading up to 
the centers of distribution of population. With these studies it will be 
possible to approximate quite closely to what may be expected regarding 
the use of current at all times in the 24 hr., and a load curve may be laid 
out and the load factor ascertained. The proper location of the central 



VARIABLE LOAD ECONOMY 



277 



station may then be picked out with reference to ease and economy of 
distribution. During the foregoing analysis the following points will 
have been considered and tentatively settled; the maximum load, the 
average yearly and daily load, the system of distribution, the location 
of the central station, the location of the various distribution lines, sub- 
stations, feeders and mains, and finally the types of prime movers. The en- 
gineer is now ready to roughly design the various parts of the system and 
to make the preliminary layouts and estimates from which the investor 
must decide as to whether the project will be commercially successful. 

Standby Losses. — In the commercial operation of a plant under change- 
able load conditions it is necessary to retain steam pressure on boilers 



„ 14 

u — — 


_^ 


— ^ J. 




|f:==:s.::; 


i.=._^..i 






2l-::d-: 


::b:=::i::iiifi 


L p. 




^^:===-^^^ 


:::":i:==bi:;; 


-N^ 





12 



Fig. 183.- 



12 12 12 12 12 

Night Night Night 

Boiler load curve of a large central heating station. 



12 Time 

(Josse.) 



which are otherwise idle in order to provide sufficient reserve capacity for 
sudden power demands and to keep up steam pressure during periods 
when the plant is shut down. Owing to radiation, leakage, and other 
losses, this requires considerable fuel. 

Take the case of an office-building plant operating 18 hr. per day. 
There are 6 hr. during which no power is being turned out. It is there- 
fore necessary either to keep up sufficient fire to maintain the normal 
boiler pressure during this period or else to close all dampers and openings 
and make up the reduced pressure before starting up the plant. Again, 
during the busy hours of the day — say from 5 to 6 o'clock when all ele- 
vators are running and, if in the winter time, nearly all the lights are 
burning — ^the power requirement reaches its maximum and all the boilers 
are operating at a high capacity. But during the light run — say 8 or 
9 o'clock on a bright summer morning — only part of the boilers are re- 
quired, and (if the plant be a large one) probably only one of the generat- 
ing sets. And, as in the case when the plant is completely shut down, 
steam pressure must be either maintained or reestabhshed before the 
boilers are brought into service. Then there are the losses due to turning 
over reserve engines preparatory to their being ''cut in," and the warm- 
ing up of idle units, etc. It will be noted that all of this requires fuel 
while not adding in any degree to the power output. The fuel losses 
caused by these conditions are known as ''standby losses" and are com- 
mon to every plant. 



278 



ENGINEERING OF POWER PLANTS 



Their magnitude depends upon the load factor, hours of operation 
per day, number of units, design and construction of plant, kind and ef- 
fectiveness of non-conducting covering, climatic conditions, etc., and is, 
therefore, a very difficult factor to accurately determine. 

For first-class plants the standby losses are probably about 6 per 
cent, of the fuel required at normal boiler rating over a period of time 



All Units 




12 2 4 6 8 10 12 2 4 6 8 10 12 
Midnight Noon Midnight 

Fig. 184. — ^Load curve of office building. 



equal to the standby period. The average is probably nearer 10 per 
cent. 

The simplest manner in which to explain this standby loss is by refer- 
ence to an actual example (see Fig. 184). 

The plant consists of two units of 75 kw. each (one of which is used 
as a reserve unit only) and one of 150 kw. rated capacity; and three 
water-tube boilers of 150 hp. each (one being for reserve purposes). The 
generating sets are high-grade, tandem-compound, self-oiling, automatic, 
direct-connected, non-condensing, piston-valve units. 

The general method of determining probable standby losses is first to 
establish the points on the load curve where different boilers should be 
cut in and out, thus dividing the day into several periods during each of 
which certain boilers are operated. From this is obtained the total 
boiler capacity idle and the number of hours of such idleness from which 
tb standby loss may be approximated in accordance with the above. 
This, of course, involves a knowledge of boiler efficiencies and engine 
economies. 

For the case in hand the exhaust steam from the engines is more than 
sufficient for furnishing heat for the building so that all the steam gener- 
ated in boilers is used by the engine and auxiliaries. Now, in order to 
determine the proper time for cutting in or out various boilers it is first 
necessary' to predetermine just when different generating units will be 
required in service. It will be noted that in the example under considera- 



VARIABLE LOAD ECONOMY 



279 



tion the entire day of 24 hr. has been divided primarily into five divisions, 
as foil - ws : 

1. From 12:00 midnight to 6:00 a.m. 

2. From 6:00 a.m. to 12:00 noon. 

3. From 12:00 noon to 4:45 p.m. 

4. From 4:45 p.m. to 7:00 p.m. 

5. From 7:00 p.m. to 12:00 midnight. 

From midnight until 6 o'clock in the morning the entire plant is out 
of service. 

The second period — that during the morning hours — is well taken 
care of by one 75-kw. set. 

During the third of these periods the maximum output is 150 kw. 




Fig. 185. — Curve of daily maximum demands. Wangen, a. A. 



and the average about 100 kw. One unit is kept in service, viz., the 
150-kw. machine. 

During the fourth period the load rapidly increases to a maximum of 
275 kw., the average being about 180 kw. One 150-kw. and one 75-kw. 
unit take care of these conditions operating at a slight overload for about 
Ihr. 

The fifth period is taken care of quite economically by the original 
150-kw. machine, the smaller unit having been shut down at 7 : 00 p.m. 



280 



ENGINEERING OF POWER PLANTS 



iiiiliiiiiiii 

1 :i\ si §|S g| §1 i| g| ^1 ^1 ai ~ 




VARIABLE LOAD ECONOMY 281 

The determination of the amount of steam required and therefore 
the number of boilers necessary at any moment is now an easy matter. 
Say for instance, the plant is started up at 6:00 a.m. with one boiler in 
service. The steam requirements are easily within the capacity of this 
boiler until the load suddenly increases late in the afternoon. At 4:00 
p.m. 100 kw. is being generated, the unit being operated at about two- 
thirds of its rated load at that instant. Assuming the steam consumption 
to be 25 lb. per indicated horsepower-hour and a combined engine and 
generator efficiency of above 90 per cent., there will at that moment be 
required steam at the rate of approximately 4,300 lb. per hour. This 
allows about 15 per cent, for auxiharies, etc., and is roughly equiva- 
lent to 145 boiler hp. This is a very small load for a good water-tube 
boiler of 150-hp. capacity, but the load increases very suddenly after 
4:00 p.m. so that it is necessary to cut in the second boiler at that 
time. 

At 6 o'clock the load has reached its maximum of 275 kw. and there 
is then required for the entire plant steam at the rate of about 12,000 lb. 
per hour or 400 boiler hp. This condition is, however, only instantaneous, 
the demand increasing and decreasing very rapidly before and after this 
time. Two 150-hp. boilers are, therefore, easily capable of caring for 
these conditions until about 10 : 00 p.m. when one boiler is cut out, leaving 
the remaining one in operation until the plant is shut down at midnight. 

It is easily seen that the day is further divided into four periods of 
operation in the boiler room which may be summarized as follows: 

1. From 12:00 midnight to 6:00 a.m., no boilers used. 

2. From 6:00 a.m. to 4:00 p.m., one boiler used. 

3. From 4:00 p.m. to 10:00 p.m., two boilers used. 

4. From 10:00 p.m. to 12:00 midnight, one boiler used. 

From this is developed the number of boiler horsepower idle during 
the day, neglecting the reserve boiler which is always idle and which is 
not considered for the reason that it is not kept under steam and therefore 
uses no fuel. 

There are two boilers idle from 12:00 midnight to 6: 00 a.m. — or 6 hr. 
each. 

There is one boiler idle, but under steam, from 6 : 00 a.m. (when plant 
is started up) until 4: 00 p.m. — or 10 hr. ; there is one boiler idle from 10: 00 
p.m. to 12:00 midnight or 2 hr. 

This is equivalent to a 150-hp. boiler idle (2 X 6) -|- 10 + 2 = 24 hr. 
If this one 150-hp. boiler were actually operating at full load for 24 hr. 
there would be developed 150 X 24 or 3,600 boiler hp.-hr. 

If oil were used as fuel and if its calorific value be 18,500 B.t.u. per 
pound and the boiler efficiency 70 per cent., there would be required 
(3,600 X 34.5 X 970) h- (336 X 18,500 X,70) 



282 



ENGINEERING OF POWER PLANTS 



barrels of oil, or 27.5 bbl. on the basis of 336 lb. per barrel. The standby 
loss is about 6 per cent, of this or about 1.65 bbl. per day. 

As a further illustration of standby losses, consider the following 




abstract of a letter ^ from John Hunter, Chief Engineer of Power Plants, 
Union Electric Light and Power Co., St. Louis, describing the practice at 
the Ashley Street Station in banking fires. 

1 Report of Committee on Prime Movers, N.E.L.A., 1914. 



VARIABLE LOAD ECONOMY 283 

"There are two general conditions under which boilers are maintained in a 
banked condition. First, boilers only required for 2 hr. at the peak in the after- 
noon and known as a short bank, where the minimum amount of coal is burned 
and where the steam pressure in the boiler is allowed to drop as low as 60 lb. 
To maintain a banked fire on a 100-sq. ft. chain grate in this condition requires 
130 lb. of coal per hour. The other condition is what is known as a long bank, 
in which about 450 lb. of coal per hour are burned on the grate and the boiler is 
kept on the header, but delivers only a small amount of steam. These boilers 
are used for varying load. 

Under present condition of operation at Ashley Street, three boilers more than 
the number required for carrying the steam load at any time are always carried 
on a long bank. With 22 boilers under fire the maximum number required on 
the load during the peak is 19 boilers. On the 528 boiler hours each day there are 
223, or 42.2 per cent., which are banking hours. 

Seventy-two of these banking hours are at the rate of 450 lb. of coal per hour 
(boilers on the long bank), consuming a total of 32,400 lb. of coal. The remain- 
ing 151 banking hours (boilers on the short bank), 'are at the rate of 130 lb. per 
hour, consuming a total of 19,630 lb. 

The total amount of coal used for banking during the 24 hr. is 52,030 lb., or 
26 tons, which at a cost of $1.10 per ton amounts to $28.60 per day. The amount 
of coal for banking amounts to 5.1 per cent, of the total consumption for the 
station. 

When notice is given of a storm existing anywhere along the transmission line, 
or when there is any possibility of an interruption in the service, standby boilers 
are started up and kept in readiness to pick up the load. The banking consump- 
tion on the standby boilers at such times will run about 450 lb. of coal per hour." 

Carrying Peak Loads Economically. — The sources of power for peak 
loads are: 

(a) Storage batteries. 

(b) Purchased power. 

(c) Hydroelectric power. 

(d) Gas engine. 

(e) Steam turbine. 
(/) Old apparatus. 

A summary of the deductions regarding each of these methods of 
meeting peak loads follows. 

(a) Storage Batteries. — Fixed charges excessive on a battery capable 
of discharging at maximum rate for 2 hr. 

(6) Purchased Power.— Heavy fixed charges per kilowatt of maximum 
demand ($15 to $25 per kilowatt) plus charge per kilowatt-hour of actual 
service. 

(c) Hydroelectric Power. — If transmitted any distance shows heavy 
fixed charges. 



284 ENGINEERING OF POWER PLANTS 

(d) Gas Engine. — ^Low fuel cost while idle, but heavy fixed charges. 

(e) Steam Turbines. — Good because of low first cost. 

(/) Old Apparatus. — Best because the interest on first cost must be 
paid or written off as depreciation. As apparatus becomes obsolete, it 
is kept a few years as peak apparatus. 

As a matter of fact any unit, no matter how uneconomical, is good 
peak apparatus since it is only used a few hours per year and the cheapest 
fixed charge determines what is best for that small amount of service. 

PROBLEMS 

69. Given a. 1,200-kw. condensing railroad unit — direct-connected type — compris- 
ing the following apparatus : 

Boilers. — Two batteries of two boilers each, three corresponding to the full rated 
capacity of the plant, one for reserve. 

Engines. — One unit — cross, compound gridiron valve type — developing rated 
capacity with 160 lb. gage pressure and 24-in. effective vacuum. 

Condensers. — Surface type, for 26.6-in. vacuum in shell, with circulating water at 
70°F. ; ratio, water to steam 40 to 1 ; head on circulating pump, 25 ft. 

Air and Circulating Pumps. — Horizontal, single, steam-driven, direct-acting. 

Feed and Oil Pumps. — Horizontal, duplex, direct-acting, steam-driven. 

Heater. — Open type, steam from feed, air and circulating pumps. 

Fuel. — Cal. crude oil, 18,500 B.t.u. per pound, 336 lb. per barrel. 

Required : 

(a) The full-load test economy of the plant in terms of kilowatt-hours output at the 
switchboard per barrel of oil burned, with constant full load. 

(6) The test economy of the plant. in terms of kilowatt-hours output at the switch- 
board per barrel of oil burned, including all standby losses, if demand on the plant is as 
follows: 

6 : 00 a.m.-8 : 00 a.m. 1,200 kw. 

8 :00 a.m.-9 :30 a.m 850 kw. 

9 :30 a.m.-3 :00 p.m 425 kw. 

3 :00 p.m.-4 :30 p.m.. . 850 kw. 

4:30 p.m.-6 :30 p.m.. 1,200 kw. 

6 : 30 p.m.-midnight 425 kw. 

Midnight-6 : 00 a.m 250 kw. 

70. Given a 1,800 kw. condensing unit — direct connected type — comprising the 
following apparatus. 

Boilers: 5 boilers of the water-tube type, 4 corresponding to the full rating of the 

plant, one in reserve. 

Engines: One unit, tandem compound type, developing rated capacity on 150 lb. 
steam and 12-in. effective vacuum. 

Condensers: Surface type, proportioned for 26.5 vacuum, with circulating water at 
70°F., ratio of water to steam 40 to 1 ; head on circulating pump, 50 ft. 

Fuel: Pittsburgh coal 13,200 B.t.u. per lb. dry; 4 per cent, moisture. 



VARIABLE LOAD ECONOMY 284a 

Required : 

(A) The full load test economy of the plant in terms of pounds of coal as fired per 
kilowatt hour with constant full load. 

(B) The test economy of the plant in terms of pounds of coal as fired per kilowatt 
hour, including all standby losses, if the demand on the plant is as follows : 

6.00 A. M. to 9.00 A. M 1,000 kw. 

Q.OO A. M. to 3.00 P. M 1,600 kw. 

3.00 P. M. to 6.30 P. M 2,000 kw. 

6.30 P. M. to 12.00 Ngt 800 kw. 

12.00 Ngt. to 6.00 A. M ;. 500 kw. 

71. A power plant consists of: 

1. A 200-hp. simple non-condensing steam engine with direct-connected 125-kw. 
D.C. generator. This unit cost complete, erected, $5,000. 

2. Two B. & W. boilers of 2,550 sq. ft. of heating surface each, costing complete 
with chain-grate stokers, erected, $9,300; two feed pumps at $200 each and feed-water 
heater costing $500. 

3. A brick stack costing $4,250. 

4. Boiler and engine houses and coal pockets costing $15,400. 

5. Incidental erecting costs $3,355. 

The output of the plant during the last year, operating 10 hr. per day for 308 days, 
was 346,000 kw.-hr. 

The plant was also called upon to supply heat 10 hr. per day for a total of 5,400 sq. 
ft. of radiation. The exhaust steam was used for heating. 

An electric company makes a proposition to supply the power at 2.5 cts. per kw.- 
hr., from its central station, the heating still to be done by the private plant. 

To take advantage of the central station power, it will be necessary to change from 
the D.C. to the A.C. system. If this is done the new A.C. motors will cost $11,500. 

About $3,675 (40 per cent, of initial cost) can be realized on the D.C. motors. The 
D.C. wiring cost $10,200. The additional wiring to change to A.C. system will 
amount to $1,870. 

The labor required during the past year consisted of one engineer at $1,100, one 
fireman at $780, one fireman 6 months at $300. 

Will it pay to purchase power and simply use the isolated plant for heating, or is 
it best to turn down the proposition of the electric company ? 

A. Cost of Operating Private Plant. 
Determine cost of: 

1. Water for power and exhaust steam heating. 

2. Water for live steam heating, if any. 

3. Coal for power and exhaust steam heating. 

4. Coal for live steam heating, if any. 

5. Oil, waste, etc. 

6. Attendance. 

7. Fixed charges. 

B. Cost with Purchased Power. 
Determine cost of : 

1. Power purchased. 

2. Water for heating. 

3. Coal for heating. 

4. Oil, waste, etc. 

5. Attendance. 

6. Fixed charges. 



2846 ENGINEERING OF POWER PLANTS 

72. It is probable that in 2 years the demand upon the plant in problem 60 will 
double the kilowatt-hour output. At the same time the manufacturing business will 
require heat 10 months, 24 hr. per day, the radiating surface amounting to 32,500 sq. 
ft. Will it pay to purchase power and run the isolated heating plant or will it be 
better to operate the isolated plant for both power and heat, adding a 500-hp. engine 
with 325-kw. D.C. direct-connected generator? The cost of this unit erected, com- 
plete, will be $15,000. The motor installations of problem 60 will be ample to take 
care of the extra demand. 



CHAPTER XIV 
COST OF POWER 

The Iron Age, July 27, 1911, gives the following figures for the cost per 
kilowatt-hour for a 2,000-hp. plant located near the colliery mouth using 
slack coal at 30 cts. per ton at the mine and 90 cts. per ton delivered. 

The plant furnished power for the railway shops and all uses of power 
were reduced to the kilowatt-hour basis. 

Output for the year 2,472,513 units (kw.-hr.) 

Coal fired 15,414 tons 

Coal per kilowatt-hour 13 . 95 lb. 

Coal per kilowatt-hour . 56 cts. 

Average yearly cost per kilowatt-hour (sta- 
tion cost) . 877 cts. 

The steam plant cost 1250,000 

Fixed charges per kilowatt-hour 1 .215 cts. 

Total cost 2.092 cts. 



28000 



24000 
22000 



^18000 

» 16000 

B 

O 14000 



W 10000 
8000 
6000 
4000 
2000 


























































\ 


















\ 


















\ 






















^^ 






















^, 


















^^ 
















T.F^ 


= 44% 


\ 


















\ 




















\ 




















\ 




















^^ 







































1000 2000 3000 4000 5000 6000 7000 80008760 

Fig. 188. — ^Load duration curve of Rochester Railway Light & Power Co. 



The Engineering Record, Jan. 21, 1911, gives the following figures for 
the station of the Edison Electric 111. Co. of Brocton, Mass.: 

285 



286 



ENGINEERING OF POWER PLANTS 



Year 


Output, 
kw.-hr. 


Use 

factor, 

per 

cent. 


Load 

factor, 

per 

cent. 


Cost of 
coal, 
cents 


Labor, 
cents 


Coal 
per ton, 
dollars 




1907.... 


2,831,000 


21.0 


26.5 


1.23 


0.34 


4.91 


Engine plant, 
1,700 kw. 


1909.... 


5,868,000 


22.3 


28.6 


0.62 


0.29 


4.45 


Turbine station, 
3,000 kw. 


1910. . . . 


8,079,000 


30.7 


33.1 


0.56 


0.29 


4.27 


Turbine station, 
3,000 kw. 



Unfortunately in America but few good steam-plant station costs are 
published on a comparable basis. In England much more publicity is 
given to these figures and Lighting and a few other papers publish in 




10 12 



Fig. 189. — ^Load curve of large central station. (Josse.) 



every issue a table of the costs, outputs, and other data for most of the 
lighting and traction plants. These figures have now been published for 
many years and are of great interest. The following tables have been 
taken from these reports. 

Stahl und Eisen, Dec. 21, 1911, pubhshed a table giving the station 
costs for 37 steam stations covering plants in Germany, Austria, Russia, 



COST OF POWER 



287 



Table Showing Cost of Power in English Electric Stations {Municipally owned) 



Electric supply 
stations 



Year 



Yearly 

load, 

kw.-hr. 



Coal 
and 
other 
fuel 



Oil, 

waste, 

water 

and 

stores 



of 
work- 
men 



Repairs 
and 
main- 
tenance 



Total 
cost 



Max. 

load 

on 

feeders 



Load 
factor 



Plant 
capac- 
ity at 
end of 
year 



St. Marylebone 

Aberdeen 

Birmingham. . . 

Bolton 

Bradford 

Brighton. 

Edenburgh 

Glasgow , 

Leeds 

Liverpool 

Manchester. . . 
Nottingham. . . 

Salford 

Sheffield 

Stalybridge. . . 

Sunderland 

West Ham. ... 



1910 
1910 
1911 
1911 
1910 
1911 
1910 
1910 
1911 
1910 
1911 
1911 
1910 
1910 
1911 
1911 
1911 



10,776,459 
5,436,065 
32,866,835 
11,156,084 
18,737,857 
10,285,680 
15,309,493 
36,479,243 
14,372,765 
36,089,627 
83,308,848 
11,944,527 
14,719,170 
10,317,933 
13,295,341 
10,208,493 
22,690,266 



586 

630 

366 

550 

325 

750 

530 

428 

305 

0.429 

0.407 

0.731 

0.530 

0.325 

0.325 

0.345 

0.470 



0406 
0203 
0203 
0408 
0610 
0460 
0407 
0407 
0203 
0407 
0203 
1420 
0610 
0203 
0202 
0202 
0203 



0.244 
0.183 
0.162 
0.163 
0.142 
0.265 
0.102 
0.184 
0.122 
0.184 
0.203 
0.285 
0.122 
0.184 
0.081 
0.122 
0.122 



.426 

183 

.245 

184 

,245 

.428 

.366 

265 

0.225 

0.143 

0.184 

0.285 

0.203 

0.325 

0.061 

0.265 

0.203 



300 

016 

793 

938 

773 

489 

039 

0.917 

0.672 

0.797 

0.814 

1.443 

0.916 

0.854 

0.487 

0.752 

0.815 



7,824 

3,218 

15,553 

5,019 

7,922 

5,140 

11,424 

21,719 

7,980 

18,071 

37,520 

6,316 

6,707 

6,870 

5,300 

5,235 

8,123 



15.72 
19.28 
24.12 
25.37 
27.00 
22.84 
15.30 
19.17 
20.56 
22.80 
25.35 
21.69 
25.05 
17.14 
28.64 
22.26 
31.89 



12,000 

4,649 

22,040 

7,600 

8,180 

7,200 

15,217 

37,478 

15,740 

37,000 

47,301 

10,850 

7,000 

11,400 

8,003 

9,590 

11,400 



Table Showing Cost of Power in English Electric Stations (Privately owned) 



Electric supply 
stations 



Year 



Yearly 

load, 

kw.-hr. 



Coal 
and 

other 
fuel . 



Oil, 
waste, 
water 

and 
stores 



Wages 

of 
work- 



Repairs 
and 
main- 
tenance 



Total 
cost 



Max. 

load 

on 

feeders 



Load 
factor 



Plant 
capac- 
ity at 
end of 
year 



Central 

Charing Cross. . . . 

Chelsea 

City of London. . . 
County of London 

London 

Metropolitan 

Westminster 

Newcastle Dist. . . 

Hackney 

Ashton on Lyne . . 

Bury 

Cambuslang 

Coventry 

Darlington 

Dewsbury 

Loughborough. . . . 

Motherwell 

Wolverhampton. . 
Prescot 



1909 
1910 
1910 
1910 
1910 
1909 
1910 
1909 
1909 
1910 
1910 
1911 
1910 
1911 
1911 
1910 
1911 
1910 
1910 
1010 



17,282,370 

25,733,222 

4,144,936 

25,183,380 

16,985,687 

10,308,537 

12,287,674 

18,546,815 

10,479,253 

4,785,053 

2,838,295 

4,014,247 

112,527 

7,443,937 

2,192,036 

1,209,675 

531,886 

2,444,944 

8,289,720 

4,560,397 



0.547 
0.770 
1.112 
0.608 
0.648 
0.709 
0.770 
1.032 
0.405 
0.528 
0.508 
0.406 
0.101 



324 
386 
527 
345 
406 
426 
345 



0.061 
0.040 
0.081 
0.020 
0.040 
0.061 
0.040 
0.101 
0.081 
0.041 
0.081 
0.041 
0.264 
0.020 
0.041 
0.081 
0.041 
0.081 
0.041 
0.041 



0.142 
0.284 
0.506 
0.243 
0.182 
0.284 
0.446 
0.304 
0.162 
0.162 
0.243 
0.142 
0.426 
0.142 
0.203 
0.406 
0.365 
0.182 
0.122 
0.162 



0.162 
0.426 
0.588 
0.304 
0.507 
0.386 
0.507 
0.467 
0.162 
0.162 
0.446 
0.182 
0.487 
0.122 
0.162 
0.609 
0.487 
0.122 
0.304 
0.162 



0.912 
1.520 
2.287 
1.175 
1.377 
1.440 
1.763 
1.904 
0.810 
0.893 



,278 
,771 
278 
608 
,792 
623 
238 
791 
893 



1 

1 



1 
1 



0.710 



8,616 

13,231 

2,769 

17,767 

10,350 

7,756 

7,800 

10,169 

5,530 

2,857 

1,391 

2,022 

120 

4,769 

1,235 

960 

355 

1,280 

4,181 

1,803 



22.90 
22.20 
17.09 
16.18 
18.73 
15.17 
17.98 
20.82 
21.63 
19.12 
23.29 
22.66 
10.70 
19.01 
20.26 
14.38 
17.10 
21.80 
22.64 
28.87 



12,830 

21,440 

3,500 

25,000 

16,500 

17,250 

18,500 

17,225 

9,000 

4,800 

1,760 

2,000 

200 

6,600 

1,970 

1,050 

600 

1,910 

5,230 

2,260 



Table Showing Cost of Power in English Electric Tramway Stations 



Electric railway 
stations 


Year 


Yearly 

load, 

kw.-hr. 


Coal and 
other 
fuel 


Oil, waste, 

water and 

stores 


Waps 
workmen 


Repairs 
and main- 
tenance 


Total 
cost 


Dublin. . 


1910 
1910 
1910 
1910 
1910 
1910 
1911 
1910 
1910 


11,771,939 

26,860,126 

14,793,687 

8,213,651 

13,960,753 

4,047,580 

4,751,903 

5,799,492 

1,596,645 


0.510 
0.245 
0.470 
0.305 
0.385 
0.590 
0.366 
0.366 
0.407 


0.041 
0.041 
0.041 
0.020 
0.020 
0.041 
0.020 
9.061 
0.020 


0.203 
0.203 
0.143 
0.184 
0.142 
0.163 
0.184 
0.203 
0.142 


0.102 

0.162 

0.041 

0.203 

0.162 

0.061 

0.470 

0.0815 

0.245 


858 


Glasgow 


651 


Leeds 


695 


Newcastle-on-Tync 

Sheffield 

Cardiff 


0.712 
0.712 
860 


Huddersfield 


1 040 


Leicester 


710 


Preston 


0.815 



288 



ENGINEERING OF POWER PLANTS 



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COST OF POWER 



289 



Coil 


i-^ ^^N ^^^ ^--"S 


^\ ^ '^-.^35 ./ -^ —^ 1 J^ 


'-'^■'-X 7- ""^^Tv f ^- -— vV f-^- 


\ . 1: Water \ ^ v^ '/ ^^>.. 


h:-^I' , -^=:-i- '^^^ 



12 

Nisht 



12 

Night 



12 

Night 



75 ^gW 
50|Ss 
25 5<=4 
H 



Fig. 190. — Curve showing water and coal consumption of a large heating station. 

(Josse.) 




Wages ^ 



5 7 9 1,000,000 12 
Yearly Load 



,9 1,00 ,000 ,12 13 MUUon 
' ' ' 'K.W.Hr. 





In 


luet 


ce of Cost c 


f Coal 








1 


Pk 


^ 


V 


--Total 


Ope 


ratio 


g cist 




! 






\ 


/ 


\ 


^ 


^-- 








, _j 


\ 


•o-o 


^ 


\ 


/ 




/ 


-^ 


<;Fuel Cost 1 










/ 


% 










1 



10 12 14 16 18 20" MUUon 
Yearly Load K.W.Hr, 

Fig. 191. — Operating cost steam power plants Fig. 192. — Influence of cost of fuel 
up to 1000 kw. capacity. (Josse.) on total operating cost. (After Josse.) 



3 


- 

- 2 
-W 
A 

-w 

ii 


\ 




























I 




























2 


\ 












^ 


al O 


)erat 


ng( 


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1 




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uel 










V 








^Sa 


arie" 


5 & 


kVage 


s 














■ — 


/^ 


ainte 


'nance 









/Lubri 


bantE 


_ 


^^ 



1 -2 
I 



10 11 12 13 14 Mimon-K.W,Hr. 

I I L 

20 MUUon i;ff.H;P."Hr. 



2 4 6 8 10 12. U IG 18 

Yearly Load 

Fig. 193. — Operating costs steam power plants, reciprocating engines and steam 

turbines. (Josse.) 



a) 1 



^2 






























-Ml 


o\ 


^ 
























-1 


»>> 


\ 


^ 


■> 










o=L 
-Total Op 


ibric 
erati 


ants 
ng C 


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93t 




d 


Main 


tena" 


-^ 


>-ft- 












. 


-Fuel 




-o 


O 


=fi= 










6 


salari^es & Wa 


jes 



7 
J L 



9 10 11 12 13 MUUon K.W.Hr. 
J 1 1 I I ] I I 



14 16 



18 



20 MlUion Eff.H.P.Hr, 



2 4 6 8 10 12 

Yearly Load 

Fig. 194. — Operating costs larger sizes of steam turbine plants. (Josse.) 



290 



ENGINEERING OF POWER PLANTS 



Sweden, Denmark and Holland. These figures are extremely interesting 
and will repay careful study. 

In his ^'Neuere Kraftanlangen," Professor Josse of Charlottenburg 
has collected figures from practically all the larger plants in Germany 
and both his figures and curves are of great value. The book also con- 
tains similar tabulations for gas and oil engines. Figs. 180 to 185 are 
reproduced from his book. 




Wage 



s, Mainteiiance Lubricatiod Packings 
in k of Total Operating Cost. 




100,000 3 



9 1.1 1.3 

Yearly Load 



1.5 1.7 Million Eff. 

H.P.«Hr. 



Fig. 195. — Curves of direct operating expenses. (Josse.) 

The following tables of station costs for stoker-fired stations and 
hand-fired stations have also been calculated in percentages for easier 
comparison. 

The following figures have been published for the station cost of tur- 
bine stations with mechanical stoking: 



Oatput 


Boston Edison 


Vitry (Paris), 
43,000,000 kw.-hr. 


Brussells 

Tramways, 

22,000,000 kw.-hr. 


Greenwich (Eng.),. 
67,000,000 kw.-hr. 




Cents Per cent. 


Cents 


Per cent. 


C,;nts 


Per cent. 


Cents 


Per cent. 


Coal 

Labor 

Oil and waste .... 

Water 

Maintenance 


0.394 
0.0897 
0.0123 
0.0079 

0.0288 


74.0 

16.8 

2.3 

1.5 

5.4 


0.46 

0.104 

0.004 

0.04 


75.6 

17.1 

0.7 

6.6 


0.389 

0.0662 

0.0125 

0.0167 


80.3 
13.66 
2.58 

3.45 


0.4731 
0.0718 
0.0159 

0.0366 


79.1 
12.0 

2.8 

6.1 


Total 


0.5327 


100.0 


0.608 


100.0 


4844 


99.99 


0.5974 


100.0 



KiLowATT-HOPR CoBTB IN STEAM-paiTBK Gewbbatino Plakts (WJlliams Bcd Tweedy). 



S'i-E 






;Twrsiir,raV.'("ft 






ESSSiSdr'l.ra" 



■0.161 U.02^ 0.032 






Int No. 5. Central ataUon during period' of o 



hIIIII 



PI&Dl No.' 21.' Ontral aUUoD (Uod"m to pl>iil No.' 1' 
PlMt No. 22. Cflntr»l sUtion (populalioo. 30.000). 
Pt^t No! 24'. 8t^t raUwa^ (populsUoa, 20.000). 



COST OF POWER 



291 



The following figures have been published for hand-fired stations with 
both engine and turbine machinery: 



Output 


Engine 

station 

Cambridge, 

7,344,392 

kw.-hr. 


Engine 
station 
Boston Edison 
kw.hr. 


Turbine 

station 

Hudson Co., 

20,000,000 

kw.-hr. 


Engine 
station, 
886,600 
kw.-hr. 


Engine 
station, 
5,952,936 
kw.-hr. 




Cents 


Per 
cent. 

47 
31 

22 


Cents 


Per 
cent. 


Cents 


Per 
cent. 


Cents 


Per 
cent. 


Cents 


Per 
cent. 


Coal 


0.46 
0.30 

0.22 


0.3750 
0.2123 
0.0279 
0.0308 
. 0406 


54.5 

31.0 

4.0 

4.5 

6.0 


0.195 
0.173 


47.2 

41.9 


1.22 

0.705 
0.031 
0.025 
0.160 


57.0 

33.0 

1.4 

1.1 

7.5 


0.575 
0.341 
0.016 
0.052 
0.070 


54.5 


Labor 

Oil and waste.. \ 

Water / 

Maintenance. . . . 


32.3 
1.5 


0.02 
0.025 


4.8 
6.1 


4.9 
6.6 










Total . . 


0.98 


100 


0.6866 


100.0 


0.413 


100.0 


2.141 


100.0 


1.054 


99.8 







It will be noticed that with stoker-fired stations the fuel cost varies 
from 74 to 80.3 per cent, of the station cost. These figures date from 
1908 to 1911 and are all from comparatively medium-sized plants, the 
plant of the Boston Edison Co. being the largest. With larger sized plants 
and 1915 conditions this percentage will probably be nearer 90 per cent, 
and for stoker-fired plants in general with turbines for prime movers it is 
safe to take the fuel cost as 80 to 85 per cent, of the station cost with 
coal at $3.00 per ton. 

In hand-fired engine stations the fuel cost varies from 47 to 57 per 
cent, of the station cost. In more modern turbine plants the percentage 
may increase to 65 or 70 per cent, with size and good operating. Sixty 
per cent, is a fair figure for estimates for a turbine plant and 50 to 55 
per cent, for an engine plant with coal at $3.00 per ton. 

Williams and Tweedy give the inserted table of kilowatt-hour cost 
of electric power in steam-driven generating plants of various sizes. 

As a general rule the better the plant, the larger the plant and the 
better the operating, the higher will be the percentage of fuel cost to the 
total station cost. 

Standards of Good Operation. — While the station cost may be used 
as a criterion of good operation, the cost of coal and its quality, the pre- 
vailing rates for labor and a number of smaller factors must be known 
before two station costs can be compared with any degree of certainty. 
For stations under the same management the station cost is a good crite- 
rion but even here there may be defects in the design of the plant which 
will prevent economical operation, or a low use factor which will greatly 
increase the unit costs. 

The coal consumption, pounds per horsepower-hour or per kilowatt- 
hour, has been used as a criterion and is a somewhat better one than 



292 



ENGINEERING OF POWER PLANTS 



station cost since only two accounts must be kept to determine it accu- 
rately and these two accounts are always kept by both large and small 
plants. The water rate per kilowatt-hour has also been used but is very 
rarely obtained with accuracy, requiring the installation of many very 
accurate water meters in the ordinary large plants. The ordinary city 
water meters can be used for the make up if calibrated very frequently. 



Station 



Output, 
kw.-hr. 



Lb., coal 

per 
kw.-hr. 



B.t.u. 
per lb. 
of coal 



B.t.u. 
per 

kw.-hr. 



L.F., 
per cent. 



Carville, 6mos. ending June 30, 1905 
Glasgow Corporation, 1905 



Manchester (Stuart Street), 1905. 
Powell-Duffryn Steam Coal Co., 1905 
City and South London Co., 1905. . . 
Charing Cross Co. Bow Stat., 1905. . 
Charing Cross Co. Bow Stat., 1904. . 

Sheffield Neepsend, 1905 

Metropolitan East Side Co., 1905. . . 

Central Co., 1905 . 

County of London Co., 1905. ...... 

Salford, 1905 

Leeds, 1906. . 

St. James & Pall Mall Co., 1905. . . . 

London Elec. Co., 1905. 

Bradford, 1905 

Westminster Co., 1905 

Berlin, 1905 

Berlin, 1904 

Vienna, 1904 

Eberfeld, 1904 

Hamburg Zollverein, 1904 

Frankfort a/Main, 1904 

Hamburg Combined, 1904 

Cohn a/Rhine, 1904 

Munich, 1904 

Copenhagen, 1904 

Charlottenburg, 1904 

Oberschlesischer Indus., 1904 

Dresden Power, 1905 

Dresden Light, 1904 

Brussells Tramways, 1907 

Buenos Ayres, 1904. 

Brocton, Mass., 1907 

Brocton, Mass., 1909 

Brocton, Mass., 1910 

Redondo, Cal., 15-day test 

Redondo, Cal., 16 mos., 1908-09 



14,604,800 

20,558,500 

28,189,455 

4,500,000 

6,644,131 

12,174,104 

10,340,657 

3,499,428 

22,711,000 

7,102,960 

11,350,000 

10,666,001 

8,436,817 

6,654,217 

14,235,423 

14,723,356 

11,616,914 

141,059,129 

113,389,947 

. 45,939,840 

7,206,950 

12,914,177 

16,431,832 

27,188,640 

13,126,850 

12,888,991 

13,280,515 

6,747,000 

27,286,995 

12,528,657 

5,464,405 

21,913,000 

32,722,381 

2,831,000 

5,868,000 

8,079,000 



3.13 

4.50 

3.57 

3.75 

4.41 

64 

43 

04 

64 

20 

50 

37 

15 



5.54 
4.60 
4.12 
4.96 
2.38 
3.10 
2.70 
3.00 
3.00 
3.30 
3.40 
3.60 
3.70 
3.90 
4.50 
4.80 
6.50 
7.20 
2.09 
3.00 
5.62 
3.21 
3.41 



11,000 
10,500 
13,500 
13,000 
11,500 
14,000 
15,000 
13,000 
11,800 
14,000 
11,000 
14,320 
11,000 
14,200 
12,000 
13,000 
14,394 
12,368 
12,576 
11,938 
12,420 
13,500 
13,500 
13,500 
12,870 
12,765 
12,519 
11,340 
10,800 
8,244 
7,560 
12,000 
13,500 
14,000 
14,000 
14,000 



34,430 
47,250 
48,200 
48,750 
50,720 
50,960 
51,450 
52,520 
54,750 
58,800 
60,500 
62,580 
78,650 
78,670 
55,200 
53,560 
71,390 
29,440 
.38,980 
32,230 
37,260 
40,500 
44,550 
45,900 
46,330 
47,230 
48,820 
51,030 
51,840 
53,580 
54,430 
25,100 
40,500 
78,800 
45,000 
47,700 
24,438 
26,200 



37.0 
17.4 
36.3 
37.0 
35.0 
13.7 
13.4 
13.4 
22.0 
12.5 
18.9 
28.0 
14.5 
18.6 
25.0 
28.0 
27.0 



30. 

31. 

35. 

27. 

38. 

29.9 

28.4 

37.8 

24.2 

29.3 

24.0 

35.2 

30.8 

22.9 

40. 0(?) 

42. 0(?) 

26.5 

26.6 

31.3 

60.0 

55.0 



COST OF POWER 



293 



Station water rates as low as 14 lb. per kilowatt-hour over a period of 
one year have been reported from stations using electric auxiliaries but 
rates from 17 to 20 lb. are very good and rates from 25 to 50 lb. or higher 
are not uncommon. Any figure between 2 and 3 lb. of coal per kilowatt- 
hour is good practice and there are very few reported figures below 2 lb. 



90000 



80000 



70000 



60000 

,^'50000 

<n 

P.40000 
H 

30000 



20000 



10000 



1 






1 

1 
































1 

1 








o = LoacJ Factors 
+ = Use Factors 
A -^ Eberswalde Fi 
















■ 





I 

1 

1 








?ures 












1 


\ 


























"i 


■ 


\ 

\ 


























1 




\ 


























\ 

6 


o ' 




\ 


























V 


Y + 


V 
























-7 


\ 


\ c 
\o 


f 

u\° 
























-8 ] 




+ V 


\ 


\ 






















-9 


V 




\ 


\ 

\ 






















-10 


\ 


^^1 


\\ 


\ 


N 
N 


^\ 






















X 


^^ 


V 


>\ 




■^■^- 






?/ = 


= ,..000 4- fT 


-15 e 

- ^1 






a' 




'^^ 


"^ 









V = 


=20^ 












^ 


-^, 






y = 


oints have been 
arily Assumed 


-30 


















Th 


jse P 
.rbitr 


-60* 






























-100% 
1 





























10 20 



80 100 



Fig.. 196.- 



40 50 60 70 
Per Cent Load Factor 
Relation between load factor and thermal units in fuel. 



per kilowatt-hour. Five pounds of coal per kilowatt-hour with very low 
load factor is good. 

Perhaps the best method of stating station economy is to give the 
B.t.u.'s in the coal per kilowatt-hour. This eliminates price and quality 
of the coal and if the load factor is stated, say 28,000 B.t.u.'s per kilowatt- 
hour at 30 per cent, load factor, we have a very good criterion of both the 
design and operation of the station. This was recognized as far back as 



294 



ENGINEERING OF POWER PLANTS 



1905 by Patchell who, in a paper in the Proceedings Institute of Electrical 
Engineers (London), vol. 39, 1905, gives the figures for a large number of 
stations. The preceding table is taken largely from Patchell's paper with 
other figures that have been published since that time. 

These values of B.t.u.'s per kilowatt-hour have been plotted as 
ordinates against load factors as abscissas in Fig. 196. The points ob- 
viously cannot he on any one curve since the stations are of all sorts 
and conditions, and the operators are of various degrees of skill, but the 
points all He in a field of elongated curved shape and the outside limits 
may be sketched in with substantial accuracy. In this field all reasonable 
values will appear. The median curve through the length of this field 
corresponds to the equation (X - 5){y - 13,000) = 665,000. 

It will be observed that good records lie to the left of the curve and 
poor records to the right. 



« s 



uou 






























^ 


1000 




























y 




9U) 
800 
■700 
600 
500 

300 


























y 




/ 






















1 






/ 
























J 




/ 


















CA^^ 


oi^ 


s^ 


^ 




/ 


/ 














2^ 


^ 












/ 










■ 


•" ' 
















/ 














y 






L.F. 






y 












^ 








100 












^ut y 




^ 










M-^tia 


^ 


at 




-= 


^^ 














-^ 


^i^-^ 


P" 























^-^50 £ 



1SU4 1905 1906 1907 1808 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 

Fig. 197. — Development curves. Detroit Edison Co. 

This measure of efficiency, B.t.u.'s per kilowatt-hour, may be turned 
into thermal efficiency by dividing it into 3,410 as shown by the second 
scale of ordinates appearing on the figure. Of the two efficiencies B.t.u.'s 
per kilowatt-hour appears to be the better to use from an operating 
standpoint since the coal is generally bought on a B.t.u. basis and the 
cost of 1,000 B.t.u's in the coal is usually well known. 

It is well to be cautious in accepting figures published in the technical 
press relating to station economy. As they usually appear they are 
mainly defective, that is, conditions are not wholly stated. A particularly 
good station cost may be quoted leaving out load factor and cost of coal. 
Sometimes the coal cost is given as lb. per kilowatt and the fact that it 
is kilowatt-hours generated and not kilowatt-hours leaving the busbars is 
not stated. As much as 10 to 20 per cent, may be used in the station. 



COST OF POWER 



295 



The loss after leaving the feeder switches should be charged to distribu- 
tion, but all losses and used current in the station are not part of output. 
Load factors should always be yearly. It would be still better if use 
factors were used but this is not general practice as yet. 

Many cost figures leave out repairs or maintenance and make no note 
of it. One com.pany bought about one-third of its output from a water- 
power company but the entire operation was charged to the steam and no 
note made of the water in the publication. In a great many cost figures 
the time over which they are taken is not stated and many excellent figures 
of days or weeks run have been published without qualification. As no 
repairs were made in this time nor oil purchased, these items do not appear. 

1,200,000 
1,100,000 



490,000 
. 4C0,000 
M 440,000 
u 420,000 
I 400,000 
% 380,000 
£ 3(30,000 
I 340,000 
a 320,000 
•S 300,000 
S 280,000 
€ 2C0,000 
= 240,000 
^. 220,(X)0 
M 200,000 
. 180,000 
§ 160,000 
^ 140,000 
•g 120.000 
I 100,000 
a 80,000 
° 60,000 
40.000 
20,000 



- 






























/ 


- 




























/ 


/_ 


- 
























.^ 


/ 


- 


- 
























^^ 


^ 




/ 


- 






















.</ 


y 




/ 


/ 


- 






















r 




/ 




/ 


- 


















A 


y 




,4 


/ 


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/ 


/ 




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/ 


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- 
















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H^.D.C.Mo 



1,000,000 



900,000 
800,000 
700,000 
600,000 
500,000 
400,000 
300,000 
200,000 
100,000 



1003 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 

Fig. 198. — Development curves, Detroit Edison Co. 

In most of these cases there is no attempt to deceive but the fault is 
due to the imperfect systems of bookkeeping and the reader must be 
able to judge of the credibility of the published figures. 

The following outline of distribution of station charges for large 
turbine plants may be used as a basis for estimating probable detailed 
operating costs by modifying the individual percentages to correspond to 
local conditions in any assumed plant. 



Operating labor: 
Boiler room . . 
Turbine room. 
Electrical .... 



Percentage of Cost Distribution 
For Large Turbine Plants 



Supervision . 



9.0 

4.0 
2.0 
2.0 



Total operating labor. 



17.0 



296 ENGINEERING OF POWER PLANTS 

Operating material: 

Coal 64.0 

Water 2.5 

Lubricants 0.5 

Miscellaneous 2.0 

Total operating material 69 . 

Total operating labor and material 86. 

Maintenance labor: 

Building 0.5 

Boiler room 1.5 

Turbine room 0.5 

Auxiliary apparatus 1.0 

Electrical : 0.5 

Piping 0.5 

Miscellaneous 0.5 

Total maintenance labor 5.0 

Maintenance material: 

Building . . ' 0-5 

Boiler room 2.5 

Turbine room 0.5 

Auxiliary apparatus 1.0 

Electrical 1.0 

Piping ; 1.0 

Miscellaneous 0.5 

Total maintenance material 7.0 

Total maintenance labor and material 12.0 

Total labor and material. 98 . 

Other charges to power station account 2.0 

100.0 

Note.— Total labor 22.0 

Total material. 76 . . 

98.0 
Other charges 2.0 

100.0 

In a paper before the A.I.E.E., Feb. 8, 1916, A. G. Christie gives the 
statistics of a number of municipal power plants in western Canada. 
The characteristics of the cities are reviewed and the costs and methods 
of financing are discussed at length. Methods of charging are also dis- 
cussed. The following table has been abstracted from the paper. The 
fuel is mostly local lignite with some Pennsylvania and Ohio bituminous 
coal. 



COST OF POWER 297 

Cost of Electric Power in Western Canadian Cities, A. G. Christie 



No. 
boilers 



No. 

turbines 



Rated 
capacity 



Installa- 
tion cost 
per kw., $ 



Output 
1,000,000 
of kw.-hr. 



Use 

factor, 

per cent. 



Coal, lb. 
per kw. 



Kamloops . 
Lethb ridge . 
Moose Jaw 
Saskatoon . 

Regina 

Edmonton . 



4 
8 
8 
8 
12 
16 



2,700 
2,300 
3,000 
5,950 
7,600 
10,250 



198.42 

118.02 

95.80 

92.70 

190.75 



9.72 

9.32 

21.93 



11.0 
17.0 
14.2 
18.6 
14.0 
24.4 



6.14 
6.9 

8.5 
4.6 
5.85 
5.25 



Fuel, 
cents 



Labor, 
cents 



Water, 
cents 



Oil, waste 

and 

supplies, 

cents 



Repairs and 

maintenance, 

cents 



Station 
cost, 
cents 



Kamloops. 
Lethbridge . 
Moose Jaw 
Saskatoon . 

Regina 

Edmonton . 



1.342 
0.369 
1.298 
1.367 
1.412 
0.754 



0.531 
0.438 
0.527 
0.326 
0.440 
0.358 



0.021 
0.045 
0.029 
0.009 
0.007 



0.041 
0.071 

0.045 
0.046 
0.033 



0.004 
0.223 

0.130 
0.087 
0.260 



1.918 
1.122 
2.010 
1.897 
1.994 
1.412 




12123456 789 10 1112 123456789 10 1112 
A.M. - - P.M. 

Fig. 199. — Yearly peak day. Load curve. The Detroit Edison Co. 
Some very interesting figures for the large Central Station Systems in 
Berlin, Chicago, and London are given by Klingenberg, Proceedings 
Institute Electrical Engineers (London), Dec. 4, 1913. The following 
table has been abstracted from his paper: 



298 



ENGINEERING OF POWER PLANTS 





Berlin (1911-12) 


Chicago (1911) 


London (1910-11) 




2,600,000 

6 

137,000 

23,000 


2,200,000 

6 

221,700 

37,000 


6,500,000 
64 


Power stations 


Installed capacity, kw 

Average size of station, kw 


298,400 
4,670 




Assets 


$38,950,000 
7,370,000 


$68,700,000 
3,435,000 


$132,700,000 


Sinking fund 


27,100,000 








31,580,000 


65,245,000 


105,600,000 




Cost per kw. installed: 


$86.45 38% 
144.00 62% 


$116.0 40% 
175.40 60% 


$160.80 45% 


Distributing system and meters. . 


193 .50 55 % 




230.45 100 


291.40 100 


354.30 100 


Peak load, kw 


94,600 
15,800 


199,300 
31,700 


185,500 


Peak load per power station, kw 


2,900 




274,000,000 


684,000,000 
32,000,000 


405,000,000 














216,300,000 


640,000,000 


319,243,000 






Comprising: 

Lighting, per cent 


24 
45 
31 


19 
12 
69 


61 


Power, per cent 


27 


Traction, per cent 


12 






Load factor (kw.-hr. generated) per 


33.1 
0.79 
1.450 
0.18 


41.0 
0.894 
1.11 
0.33 


24.9 


Ratio, kw.-hr. sold to kw.-hr. generated 
Reserve factor . 


0.788 
1.61 


Use factor (total) . . ' 


0.122 






Coal, price per ton 


$4.22 
3.015 
9.7 


$1.94 
3.54 
7.6 


$3.10 


Coal consumption per kw.-hr. sold, lb. 


5.21 
5.0 








$8,325,000 
4,280,000 


$14,020,000 
7,000,000 


$15,130,000 




6,750,000 






Profit absolute 


4,045,000 
12.83 


7,020,000 
10.87 


8,380,000 


Percentage of real value 


7.85 








3.84 


2.19 


4.74 






Opera 
Expenses: 

Fuel 


ting costs per kw.-hr. 

. 58 cts. 

0.0945 

0.1235 

0.227 

0.0844 

0.2035 

0.744 


sold 

0.2781 cts. 

0.0109 

0.149 

0.201 

0.1465 

0.2015 

0.0405 

0.0657 


0.74 cts. 




0.0635 


Wages... 


0.254 


Repairs, maintenance 


0.359 


Rent, taxes, insurance 


0.359 




0.338 






JMtinicipal participation . . . 










2.057 


1.093 


2.11 






Profit gross 


1.78 


1.098 


2.63 







1 Kw.-hr. sold includes kw.-hr. purchased; therefore the actual value is 4 to 5 per cent, higher. 



COST OF POWER 



299 



The Cost of Electric Power in New York City. — The tables following, 
which are compiled from two articles published in Engineering Contracting 
for Apr. 6 to May 11, 1910, give unit costs of generating and distributing 
electricity for power and lighting in the plants of the Edison Electric 
Illuminating Co. of Brooklyn and the New York Edison Co. during the 
fiscal year ending June 30, 1907. The New York Edison Co. produces 
nearly 70 per cent, of the electricity used for lighting in New York City 
and the Brooklyn Co. is by far the most important operating in the city, 
next to the New York Edison Co. The combined capacities of the plants 
of the two companies aggregated nearly 132,000 kw. 



Cost of the Brooklyn Plant 



Total 



Per kilowatt 



Generating station buildings and land 

Substation buildings and land 

Other real estate 

Steam plant, generating station 

Electrical plant, generation station 

Substation apparatus 

Transmission lines 

Construction, subways 

Services 

Line transformers . 

Meters 

Arc lamps 

Tools and implements 

Office furniture and fixtures 

Miscellaneous appliances 

Storage batteries » 

Sundries, automobiles, etc 

Total 



$674,666 

650,559 

48,007 

1,051,796 

965,824 

507,965 

4,136,009 

230,950 

973,558 

150,184 

301,677 

242,607 

20,955 

50,131 

64,874 

182,150 

74,526 

$10,326,437 



$29 

28 

2 

44 

41 

21 

175 

10 

41 

6 

13 

10 

1 

2 

3 



$437 



Production and Sale of Current 



Brooklyn 



New York 



Kilowatt-hours produced 

Kilowatt-hours used in station 

Kilowatt-hours sold 

Average load factor, per cent 

Transmission losses, etc., per cent. . 
Average sale price, cents per kw.-hr 



71,769,804 
800,783 

47,912,138 
34.7 
32.5 
6.6 



299,172,431 



209,024,002 
31.5 
30.0 
6.49 



300 



ENGINEERING OF POWER PLANTS 



Cost of Power Generation and Distribution 
Production Expense 



Brooklyn 



Total 



Cents per 
kw.-hr. 



New York 



Total 



Cents per 
kw.-hr. 



Salaries 

Labor 

Fuel 

Oil, waste and sundries 

Water 

Repairs, building and structures 

Repairs, motive power 

Repairs, electrical apparatus . . . . 

Station expense 

Purchased power, electric 

Total production expense 



$22,510 
136,116 

285,654 

17,355 

28,449 

2,493 

39,622 

2,296 

2,330 

28,575 



$565,400 



0.031 
0.190 
0.400 
0.024 
0.039 
0.005 
0.056 
0.003 
0.003 
0.039 

0.788 



$35,908 

508,778 

1,210,599 

54,565 

135,211 
37,435 

211,175 
22,634 
24,893 
75,220 



$2,316,418 



0.012 
0.171 
0.406 
0.018 
0.045 
0.012 
0.070 
0.007 
0.008 
0.025 

0.774 



Distribution Expense 



Salaries 

Substation labor and expense 

Rental of conduits, etc * 

Incandescent lamp renewals 

Wiring and jobbing 

Repairs, poles and lines 

Repairs, subways and cables 

Repairs, meters 

Repairs, transformers 

Repairs, substations 

Repairs and expense, commercial lamps . 
Repairs and expense, street lamps 



Total distribution expense . 



$7,687 

98,607 

117,162 

110,199 



22,918 
30,957 

4,872 
187 



89,711 



$482,300 



0.011 
0.138 
0.163 
0.153 

0.032 
0.043 
0.007 



0.125 



0.672 



$64,146 

148,499 

1,014,081 

528,213 

139,713 

21,716 

56,856 

221,894 

202,611 

12,872 
68,096 



$2,388,698 



0.021 
0.050 
0.339 
0.147 
0.047 
0.007 
0.019 
0.074 

0.068 
0.004 
0.023 

0.799 



COST OF POWER 

General Expense 



301 



Brooklyn 



Total 



Cents per 
kw.-hr. 



New York 



Total 



Cents per 
kw.-hr. 



Salaries of officers 

Salaries of office staff 

Collecting and reading meters . 

Office expense 

Legal expense 

General expense 

Advertising and soliciting 

Advertising 

Canvassing new business 

Insurance 

Engineering and testing 

Leaseholds, rentals, etc 

Miscellaneous 



$18,850 
67,665 
19,797 

19,009 
73,256 

44,364 

82,917 
47,884 



58,178 



Total general expense $431,920 



0.029 
0.094 
0.028 

0.027 
0.101 

0.061 
0.115 
0.067 



0.080 



0.602 



$51,241 
335,825 

294,009 
116,630 

218,850 



118,393 
78,707 
47,656 



0.017 
0.113 

0.098 
0.039 



$1,262,311 



0.073 



0.040 
0.026 
0.016 



0.422 



Taxes and Miscellaneous 






Taxes, general 


86,916 
61,584 

4,783 


0.121 
0.085 
0.007 

0.213 


702,628 

35,464 
1,721,413 


0.235 


State franchise tax 




Leaseholds, rentals, etc 




XJncoUectable bills . . . 


Oil 


Depreciation and contingent expense .... 


0.575 


Total taxes and miscellaneous. . . 


$153,283 


$2,459,505 


821 







Summary 



Total production expense 

Total distribution expense .... 

Total general expense 

Total taxes and miscellaneous. 

Grand total 



$565,430 
482,300 
431,920 
153,283 



$1,632,903 



0.788 
0.672 
0.602 
0.213 

2.275 



$2,316,418 
2,388,698 
1,262,311 
2,459,505 



$8,425,932 



0.774 
0.799 
0.422 
0.821 

2.816 



Load Curves. — The accompanying load curves and records of con- 
nected load illustrate the rapid increase in generating-plant capacity 
which has had to be provided to keep pace with the growing demand. 
The recent development of Detroit as a factory city is responsible 
in a measure for the unusual increase of commercial load, and the 
resulting influx of factory employees has developed the residence service 
in the newer sections. 



302 



ENGINEERING OF POWER PLANTS 



Figure 198 records the increase in total kilowatt-hours' output, total 
commercial kilowatts connected, number of meters, and the total 
horsepower of motors, both direct-current and alternating-current, for 
the years 1903 to 1919. 

In addition to its own hghting and commercial load, the Detroit sys- 
tem furnishes energy for the associated Eastern Michigan Edison Co., 
operating in the suburban district surrounding Detroit. About one-fifth 
of its total generated output is purchased by the Detroit city railways for 
operating cars in all outlying sections of the city. Another unusual trac- 
tion load taken over by the central-station company within the year is 
the operation of the Detroit River tunnel of the Michigan Central Rail- 
road. The tunnel substation takes its energy supply through a 500-kw. 
motor-generator set, being arranged with a storage battery so that the 



8>,0Q0^00a 

7,ooa.ooo 

6,000,000 
5,000,000 
4,000,.000 
3^000,000 
2.„000,000 
1,000,000 
Q 



<^ 




<>% 



■^\ 



1903 1904. 1905 1906 1907 .1908 1909 1910 



Fig. 200. — Development curve, 
Melbourne Elec. supply. 



3500 
30OO 












A 


\ 




2500 
2000 












/^ 


u 


\ 






« 


r^ 


\/ 


/ 


\ 


\ 


1500 








nj>r- 


w 


/f 




k\ 


lODO 








' 1% 


(J ~ _^ 


J-r 


\V 




■^ 


— 




'^m 


1^ 


J 


\N 


600 


r'^: 


i^ 










^-r ' 













32 



12 
Noon 



Fig. 201. — Load curve of maximum days, 
Melbourne Elec. supply. 



peaks of demand of train acceleration are not felt by the central-station 
system. 

Figure 197 shows the continuation of growth in its relation to popula- 
tion, and similar curves are given in Figs. 200, 201 and 202 for Melbourne, 
Australia. 

Curves of daily maximum loads show the variation of demand 
throughout the year and should be studied very carefully as much may 
be learned from them. 

Cost Curves at Variable Loads. — Dr. Khngenberg, in ''Bau. Gr. 
Elek.," has shown a very convenient method for showing graphically the 
economy of central stations. This is possible where it is convenient to 
get the actual cost at two or three ratings over a sufficient period of time 
to reduce errors to small dimensions. 

If the total cost in dollars, including fixed charges, is plotted as ordi- 
nates, against the load in kilowatts as abscissae, the resulting curve will be 
a straight line intercepting the F-axis at a fixed distance above the origin. 



COST OF POWER 



303 



If the cost curve be transposed, making the F-axis the X-axis, extend 
the new X-axis to the right and erect upon this a daily load curve, 
the hourly cost can be read off directly with suitable scales at any 
portion of the curve. 



1„ 000^000 
900^000 
800.000 
































^ 


-^ 


^ 


\, 
















/ 








\ 


<^ 


?9, 










^ 


/ 


-^ 


y 


\ 


i^o. 




^ 









600,000 


/ 




[/ 








^ 










/ 








y 




4.. 








'^ 


400.000 






A 










7q 










M 


' ' 










^ 


^ 


ht- 








200.000 

100,000 













































































a <f 



Fig. 202. — Curves of monthly outputs, 
Melbourne Elec, Supply. 




Daily Load K.W. His. 

Fig. 203. — Coal consumption curve, 
Markische E. W. 



If the intercept of the economy curve be transferred to the F-axis 
below the origin and each point of the load curve be projected to the econ- 
omy curve and thence transferred to the fourth angle, as in Fig. 196, an 



.|.1600 
21400 



a 1200 
•I 



a 600 
I 400 



























































/ 


















y 


















X 
















y' 


y' 
















;^ 


/■ 
















A 
















y 


/ 


















y 





















WW 

450 
400 

^350 

o 
Q 
S 300 

PI 250 

I2OO 

,|l50 

100 

50 






































/ 


' 
















/ 


/ 














./ 


/ 
















A 


/' 
















V 


/ 
















7 
















J 


r 


















/f 









































Daily Load K.W. Hrs. 

Fig. 204. — Steam consumption curve, 
Markische E. W. 



Daily Load K.W. Hrs. 

Fig. 205. — Station cost curve, 
Markische E. W. 



area will result whose ordinates will be cost and from which the constant 
and variable costs can be scaled off for any hour of the day. 

If yearly records are available and a plot be made with the economy 
curve in the second angle and the average load of each hour of the year 



304 



ENGINEERING OF POWER PLANTS 



plotted in the first angle in the order of their magnitude, commencing 
with the maximum hour, and these two curves be combined as before in 
the fourth angle, a yearly cost curve will be obtained. The area under 
the yearly load curve in the first angle will be the output of the station 
in kilowatt-hours and the shape of the curve will show how much the 
machinery is used and to what advantage. Similar curves may be drawn 
for the yearly steam consumption and coal consumption. 

In London Engineering, Nov. 13, 1914, R. H. Parsons has shown curves 
of a similar character, but not so well developed, and S. A. Fletcher, in 
the Electric Journal, has done similar work along this line. It should be 
noted that the diagrams show that the smaller the use factor the greater 
will be the effect of the constant cost portion of the area under the curve. 
The full-load efficiency of the machines, which is often the criterion, will 




Fig. 206. 



influence but little the cost of production. To obtain the most econom- 
ical results we must aim at the reduction of the three factors, invested 
capital, constant operating losses and the attendance cost. This saving 
is to be sought by means of correct design and arrangement, but not at the 
expense of quality and safety. The constant portion of the load should 
be carried by the most economical machines, reserving the cheaper equip- 
ment for the variable portion of the load. Figs. 197 and 198 give oper- 
ating results on this basis for one of the most interesting of central 
stations. 

On pages 66 to 73 of the same book. Dr. Klingenberg has estimated 
the cost and calculated the station economy for three different sizes of 
power plants, 1,000-kw., 5,000-kw. and 20,000 kw. He has worked these 



COST OF POWER 



305 



figures out on the basis of various use factors from 10 per cent, to the lim- 
iting condition, 100 per cent., and his results, which are shown in Figs. 
199 and 200, are very interesting. These curves are analogous to the 
economy curve for steam engines, given so long ago by Emery. 




Cost 



Hrs. 



Total Yearly 
Steam Consumption 



Fig. 207. 



§ w 

21 

. 20 

^ i 18 

a M 

a "\ 

2 17 
in 

16 



1.00 





\ 








w 










50000 ^. 




£ 


'^LOon^ 


imption 


w 










B.T. 


% 








1 


^^^ 








ump 


X: 


5:^. 






1 




"-"^^ 


^^at£on 


pumption 


20000 1 








"es 












\. 








E 
8 S 


% 




■Bvajfl 


aUoO_^ 


« 

^ 




><j 


p^.i^ X 




7 § 


^ 






ir. 


2 


/ 








6 H 











0.1 0.2 0.3 0.4 0.5 

Use Factor 

Fig. 208. — Economical results Eberswalde Station, Markische E. W. 



In ^'Bau. Gr. Elek.'' he has given figures regarding the Eberswalde 
plant of the Markischer Elektrizitatswerke. This plant, illustrated in 
Figs. 96 and 160, had 7,400 kw. installed in 1,500-r.p.m. turbines at that 



306 



ENGINEERING OF POWER PLANTS 



time and cost $393,000 including $7,150 for land and bulkhead work. 
This is the cheapest central station reported and is a fine example of 
clever design, being well suited to the work expected of it. The cost per 
kilowatt installed is $53 and the fixed charges at 12 per cent, are $47,100 
or $6.36 per kilowatt. Very careful records were kept for the 3-year 
period which the figures cover and the following table indicates first-class 
results following careful design and good operation. 



Use 
factor, 
per cent. 


Coal, lb. 

per 
kw.-hr. 


B.t.u.'s 

per 
kw.-hr. 


Lb. water 
evaporated 
per lb. coal 


station 
water 
rate 


Operating 
cost 


Fixed 

charges, 

12 per cent. 


Total 

station 

cost 


10 


3.24 


41,200 


6.72 


21.76 


0.794 


0.726 


1.520 


20 


2.495 


31,700 


7.47 . 


18.66 


0.590 


0.363 


0.953 


30 


2.247 


28,533 


7.83 


17.63 


0.523 


0.242 


0.765 


40 


2.133 


26,950 


8.05 


17.11 


0.490 


0.181 


0.671 


50 


2.048 


26,000 


8.20 


16.80 


0.466 


0.145 


0.611 



Economizers are used in this station but no heaters. The auxiliaries 
are electrically driven with the exception of the feed pumps and condenser 
pumps which are driven by small steam turbines. 

Table 1. — Klingenberg's Estimate 



No. 



Items 



Power plants 



A = 20,000 kw. B = 5,000 kw. C = 1 ,000 kw, 



Boiler eff. full load including power for draft, 

chain grates and feed pumps, % 

No-load boiler consumption i-n per cent, full load 

Boiler, % 

Auxiliaries, % 

Feed pumps, % 

Total, % 

Heat drop in turb. and cond. (185#-197° S.H.) 

B.t.u./# 

Steam at full load including excit. and aux., 

#/kw.-hr 

Heat equiv. of 1 kw.-hr., B.t.u 

Eff. of turb. = item 5 -v- (item 3 X item 4) , % 

No-load cons, per cent, full-load consumption, % 

Live-steam piping surface, sq. ft 

Heat loss, B.t.u./sq. ft./hr 

Eff. of piping excl. of throttle loss, % 

Power cons. (light,etc.,in station") in % full load, % 

Installation cost per kw., $ 

Water, etc., per kw. year, $ 

Wages per kw. year, $ 

Repairs per kw. year (1 % station cost), $ 

Interest & renewals per kw. year (12 % sta. cost) $ 

Heating value of coal, B.t.u./jf, 

Cost of coal delivered to boiler per ton (2,000 #) . . 
Cost per million B.t.u., $ 



20 



78 



76 



75 



9.00 


9.75 


10.00 


1.50 


1.50 


1.50 


0.50 


0.50 


0.50 


11.00 


11.75 


12.00 


1,240 


1,240 


1,240 


12.8 


14.3 


16.5 


3,415 


3,415 


3,415 


21.5 


19.1 


16.6 


10.0 


12.5 


15.0 


1,940 


1,400 


1,076 


368 


368 


368 


99.8 


99.7 


99.6 


0.5 


0.75 


1.00 


35.70 


47.60 


71.40 


0.07 


0.10 


0.14 


0.70 


1.00 


1.43 


0.36 


0.48 


0.73 


4.28 


5.71 


8.56 


13,500 


13,500 


13,500 


3.24 


3.24 


3.24 


0.12 


0.12 


0.12 



COST OF POWER 



307 



Table 2 



' 


Items 


Heat consumption of plants at full load 


No. 


A = 20,000 kw. 


B = 5,000 kw. 


C = 1,000 kw. 




Con- 
stant 
part 


Vari- 
able 
part 


Total 


Con- 
stant 
part 


Vari- 
able 
part 


Total 


Con- 
stant 
part 


Vari 
able 
part 


Total 


20 


Boiler (1-2) 


11.00 


89.00 


100.00 
78.00 


11.75 


88.25 


100.00 
76.00 


12.00 


88.00 


100.00 






75.00 






















21 


Piping (10) 
Received 


0.16 


77.84 


78.00 

77.84 


0.23 


75.77 


76.00 

75.77 


0.30 


74.70 


75 00 




Delivered . . 


74.70 




















22 


Turbine (6-7) 
Received 


7.78 


70.06 


77.84 
16.70 


9.45 


66.32 


75.77 
14.50 


11.20 


63.50 


74.70 




Delivered 


12.40 




















23 


Light and power 
Received 


0.0& 


16.62 


16.70 
16.62 


0.11 


14.39 


14.50 
14.39 


0.12 


12.28 


12.40 




Delivered 


12.28 




















24 


Total balance 


19.02 


80.98 


100.00 
16.62 


21.54 


78.46 


100.00 
14.39 


23.62 


76.38 


100 . 00 






12.38 




















25 


Total balance per kw.-hr. full 
load 

Received, B.t.u 

Delivered, B.t.u 


3,900 


16,600 


20,500 
3,415 


5,150 


18,600 


23,750 
3,415 


6,580 


21,220 


27,800 
3,415 




















26 


Coal per kw.-hr., # 


0.29 


1.23 


1.52 


0.38 


1.38 


1.76 


0.49 


1.57 


2.06 



Table 3 





Items 


Operating cost in cents per kw.-hr. at full load 


No. 


A = 20,000 kw. 


B = 5,000 kw. 


C = 1,000 kw. 




Constant 
part 


Variable 
part 


Total 


Constant 
part 


Variable 
part 


Total 


Constant 
part 


Variable 
part 


Total 


27 
28 
29 
30 
31 


Coal (19-25) . . 
Water (13) .... 

Wages 

Repairs 

Interest and 

renewals 

Total 


0.047 
0.001 
0.008 
0.004 

0.049 
0.109 


0.199 
0.199 


0.246 
0.001 
0.008 
0.004 

0.049 
0.308 


0.062 
0.001 
0.011 
0.005 

0.065 
0.144 


0.223 
0.223 


0.285 
0.001 
0.011 
0.005 

0.065 
0.367 


0.079 
0.002 
0.016 
0.008 

0.098 
0.203 


0.255 
0.255 


0.334 
0.002 
0.016 
0.008 

0.098 
0.458 



308 



ENGINEERING OF POWER PLANTS 



Table 4 



Items 



Units 



Symbol 



Power plant 



A 
20.000 kw. 



B 
5,000 kw. 



C 
1,000 kw. 



Heat consumption at no load (25') 
Additional heat consumption (25) 
Operatingcost withoutcoal (32) (27) 
Cost of coal (19) 



B.t.u. per kw.-hr. 
B.t.u. per kw.-hr. 
Cents per kw.-hr. 
Cents per mill B.t.u. 



3,900 

16,600 

0.062 

12 



5,150 

18,600 

0.082 

12 



6,580 

21,220 

0.124 

12 



Table 5 



No. 



Items 



Units 



Power plant 



20,000 kw. 



B = 5,000 kw. 



C = 1,000 kw. 



Momentary heat con- 
sumption, B.t.u./kw.-hr. 



Tr« = 3,900— +16,600 



PFt = 5, 150— + 18,600 



Prt = 6,580— + 21,220 
m 



Average yearly heat con- 
sumption, B.t.u./kw.-hr. 



TFm = 3,900-/ +16,600 



TFm = 5,150-7+18,600 



Wm = 6,580-7+21.220 



If (7 = 1), B.t.u./kw.-hr. 



Tfmi = 3,900- +16,600 
n 



Tfmi = 5, 150- + 18,600 
n 



TFoti = 6,580- + 21,220 



If (f = n), B.t.u./kw.-hr. 



PFm2 = 20,500 



TFm2 = 23,750 



TFw2 = 27,800 



Average yearly operating 
cost, cents/kw.-hr 



ir = 0.062l + 12XT^. 



n 1,000,000 



2^ = 0.0821 + 1^^1:^-- 
n 1,000,000 



7v=0.124l+-12X^' 



n 1,000,000 



Table 6 





Limit / = 1 


, n = m Equation #5 




Limit 7 


= n Equation #6 


Use factor 


B.t.u. per kw.-hr. 


Percentage 
20,500 = 100% 


B.t. 


u. per kw 


-hr. 




A 


B 


C 


A 


B 


C 


, A 


B 


C 


1.0 


20,500 


23,750 


27,800 


100.0 


86.1 


74.0 


20,500 


23,750 


27,800 


0.9 


20,930 


24,320 


28,520 


98.0 


84.2 


72.1 


20,500 


23,750 


27,800 


0.8 


21,470 


25,020 


29,420 


95.5 


81.9 


69.6 


20,500 


23,750 


27,800 


0.7 


22,170 


24,950 


30,620 


91.8 


79.0 


67.0 


20,500 


23,750 


27,800 


0.6 


23,100 


27,170 


32,170 


88.9 


75.6 


63.8 


20,500 


23,750 


27,800 


0.5 


24,400 


28,900 


34,420 


84.1 


71.0 


59.8 


20,500 


23,750 


27,800 


0.4 


26,350 


31,500 


37,670 


77.9 


65.2 


54.7 


20,500 


23,750 


27,800 


0.3 


29,600 


35,800 


43,120 


69.4 


57.2 


47.5 


20,500 


23,750 


27,800 


0.2 


36,100 


44,400 


54,020 


56.7 


46.4 


37.9 


20,500 


23,750 


27,800 


0.1 


55,600 


70,100 


86,920 


36.8 


29.3 


23.6 


20,500 


23,750 


27,800 



COST OF POWER 
Table 7 



309 



A 
0.062 

n 


B 

0.082 
n 


c 

0.124 

n 


A 

12 X Wm 
1,000,000 


B 

12 X Wm 

1,000,000 


C 

12 X Wm 

1,000,000 


0.062 


0.082 


0.124 


0.246 


0.285 


0.334 


0.069 


0.091 


0.138 


0.252 


0.292 


0.342 


0.078 


0.102 


0.155 


0.258 


0.300 


0.352 


0.089 


0.117 


0.177 


0.266 


0.312 


0.368 


0.103 


0.137 


0.207 


0.278 


0.326 


0.386 


0.124 


0.164 


0.248 


0.293 


0.347 


0.413 


0.155 


0.205 


0.310 


0.316 


0.378 


0.452 


0.206 


0.273 


0.413 


0.356 


0.430 


0.517 


0.310 


0.410 


0.620 


0.433 


0.535 


0.650 


0.620 


0.820 


1.240 


0.667 


0.840 


1.040 







Table 7 {Continued) 








Limit / = 


■- 1 Equations 5 and 7 


Limit / = 


= n Equations 6 and 7 


Use factor 


Power plant 


Power plant 




A 
20,000 kw. 

cts./kw.-hr. 


B 

5.000 kw. 
cts./kw.-hr. 


C 

1,000 kw. 
cts./kw.-hr. 


A 

20.000 kw. 
cts./kw.-hr. 


B 

5,000 kw. 
cts./kw.-hr. 


C 

1.000 kw. 

cts./kw.-hr. 


1.0 


0.308 


0.370 


0.458 


0.308 


0.369 


0.458 


0.9 


0.321 


0.385 


0.480 


0.315 


0.379 


0.472 


0.8 


0.336 


0.406 


0.507 


0.324 


0.390 


0.489 


0.7 


0.357 


0.431 


0.545 


0.335 


0.408 


0.511 


0.6 


0.381 


0.463 


0.593 


0.349 


0.425 


0.541 


0.5 


0.417 


0.514 


0.661 


0.370 


0.452 


0.582 


0.4 


0.471 


0.586 


0.762 


0.401 


0.493 


0.644 


0.3 


0.562 


0.706 


0.930 


0.452 


0.564 


0.747 


0.2 


0.743 


0.948 


1.270 


0.556 


0.703 


0.954 


0.1 


1.287 


1.660 


2.280 


0.866 


1.105 


1.574 



Annual Cost of Power. — Harrington Emerson says:^ 

"In China men are paid $0.01 an hour for climbing treadmills actuating stern 
wheels which propel river boats. These Coolies convert their stored human 
muscular energy into mechanical foot-pounds. From experience with treadmills 
in British prisons we know exactly the mechanical equivalent of hard labor. It 
is a climb of 8,640 ft. each 24 hr. This is the limit of human endurance for a 
succession of days. To convert this into horsepower we must know the man's 
weight and the number of hours he works each day. The average weight of man 
is about 150 lb. A man of this weight climbing 8,640 ft. in 24 hr. yields 1,296,000 
ft.-lb. A horsepower for 24 hr. is 47,530,000 ft.-lb. It would therefore take 
36.6 Chinamen to yield a continuous horsepower and the wages of these China- 
men would amount to $3.66 per day, or $1,336 a year. 

''From Niagara you can buy a horsepower year for $20. It costs the paper 
mills which have their own power about $12 a year for continuous horsepower. 

1 Proceedings S.P.E.E., vol. 20, 1912. 



310 



ENGINEERING OF POWER PLANTS 



Human energy at $0.10 a day costs one hundred and ten times as much as this 
water-power energy, although the supervising human labor receives an average 
of $3 a day. 

"The substitution of uncarnate energy for human muscular energy has in- 
creased wages thirty-fold and has cheapened power to 1 per cent, of its cheapest 
muscular price. This is not all. When men are used as power generators the 
supply is strictly limited and can be easily monopolized. Uncarnate energy is 

90000 
85000 



75000 
70000 







0.1 0.2 0.3 0.4 0.5 0,6 0.7 0.8 0.9 1.0 
Us3 Factor 
For(/=l)Heavy Lines For{/=M)Light Weight Lines 

Fig. 209. — Klingenberg's cost curves. 



0.1 0.2 0,3 0.4 0.5 0,6 0.7 0.8 0,9 1.0 
Use Factor 
For{/=l) Heavy Lines For (^^^w) Light WeigM Lines 

Fig. 210. — Klingenberg's heat consump- 
tion curve. 



without limit as long as there is coal and oil and gas, as long as the sun shines and 
makes organic fuels or draws up water from the surface of the ocean. 

"For strictly limited horsepower at $1,336 a year we now have unlimited horse- 
power at a minimum price of $12." 

Although the cost of a horsepower varies greatly with local conditions 
and with the cost of fuel, water, labor and supplies yet a fair idea of the 
average cost may be obtained from the following tables prepared by 
different students of power costs. 



COST OF POWER 



311 



Yearly Costs of Steam Power, 308 Days, 10 Hr. per Day, Simple Non-con- 
densing Engine 
Table A. — Engine and Boiler Combined 



Horsepower of engine 

Total coal consumption in pounds per horse- 
power-hour 

Cost of plant per horsepower 

Fixed charges on plant at 11 per cent $ 

Cost of coal at $5 per long ton $ 

Attendance $ 

Oil, waste and supplies $ 

Total yearly cost, coal at $5 per ton $ 

Total yearly cost, coal at $4 per ton .......$ 

Total yearly cost, coal at $3 per ton $ 

Yearly cost per horsepower, coal at $5 per ton . % 
Yearly cost per horsepower, coal at $4 per ton . $ 
Yearly cost per horsepower, coal at $3 per ton . % 



13.0 
200.00 

44.00 
180.00 

99.00 

13.20 
336.00 
300.00 
265,00 
168.00 
152.00 
132.00 



10.50 
152.00 

50.00 
215.00 
109.00 

14.30 
388.00 
345.00 
300.00 
130.00 
116.00 
102.00 



133 

58 

233 

116 

15 

424 

385 

340 

106 

95 

83 



7, 

110, 

72, 

325, 

136. 

17, 

550, 

495, 

430, 

92, 

81, 

72, 



78 

420 

154 

20 

672 

610 

530 

84 

76 

66 



10 



12 

7.25 

78.00 

102.00 

600.00 

184.00 

23.80 

910.00 

810.00 

710.00 

76.00 

68.00 

59.00 



Table B. — Engine and Boiler — Independent 



Horsepower of engine 

Total coal consumption in pounds per horse- 
power-hour 

Cost of plant per horsepower $ 

Fixed charges on plant at 11 per cent $ 

Cost of coal at $5 per long ton $ 

Attendance $ 

Oil, waste and supplies $ 

Total yearly cost, coal at $5 per ton $ 

Total yearly cost, coal at $4 per ton $ 

Total yearly cost, coal at $3 per ton $ 

Yearly cost per horsepower, coal at $5 per ton.S 
Yearly cost per horsepower, coal at $4 per ton . $ 
Yearly cost per horsepower, coal at $3 per ton.$ 



10 

7.40 

210.00 

230.00 

510.00 

173.00 

22.00 

935.00 

840.00 

740.00 

93.50 

84.00 

74.00 



12 

7.25 

194.00 

255.00 

600.00 

184.00 

23.80 

1,063.00 

960.00 

830.00 

88.00 

79.00 

68.00 



14 

7.00 

182.00 

280.00 

675.00 

194.00 

25.80 

1,175.00 

1,050.00 

920.00 

83.00 

74.00 

64.00 



15 

6.50 

174.00 

285.00 

690 . 00 

202.00 

26.50 

1,203.00 

1,080.00 

950.00 

80.00 

72.00 

62.00 



20 

6.00 

153.00 

337.00 

830 . 00 

230.00 

31.20 

1,428.00 

1,260.00 

1,100.00 

71.00 

64.00 

56.00 



Table B {Continued) 



Horsepower of engine 

Total coal consumption in pounds per horsepower-hour . . . 

Cost of plant per horsepower $ 

Fixed charges on plant at 11 per cent % 

Cost of coal at $5 per long ton $ 

Attendance $ 

Oil, waste and supplies % 

Total yearly cost, coal at $5 per ton $ 

Total yearly cost, coal at $4 per ton $ 

Total yearly cost, coal at $3 per ton $ 

Yearly cost per horsepower, coal at $5 per ton $ 

Yearly cost per horsepower, coal at $4 per ton $ 

Yearly cost per horsepower, coal at $3 per ton $ 



30 

5.50 

126.00 

415.00 

1,100.00 

287.00 

41.50 

18.43 

1,660.00 

1,450.00 

60.00 

54.00 

47.00 



40 

4.75 

107.00 

475.00 

1,310.00 

338.00 

51.00 

2,194.00 

1,960.00 

1,710 00 

55.00 

49.00 

42.00 



50 

4.50 

96.00 

525.00 

1,540.00 

390.00 

61.50 

2,516.00 

2,250.00 

1,960.00 

50.00 

45.00 

39.00 



75 

4.00 

79.00 

650.00 

2,050.00 

520.00 

86.00 

3,306.00 

3,000.00 

2,650.00 

44.00 

39.00 

34.00 



312 



ENGINEERING OF POWER PLANTS 



Table C 



Horsepower of engine 

Total coal per horsepower per hour, pounds 

Cost of plant per horsepower $ 

Fixed charges on plant at 11 per cent $ 

Cost of coal at $5 per long ton $ 

Attendance $ 

Oil, waste and supplies $ 

Total yearly cost, coal at $5 per ton $ 

Total yearly cost, coal at $4 per ton $ 

Total yearly cost, coal at $3 per ton $ 

Yearly cost per horsepower, coal at $5 per ton . . $ 
Yearly cost per horsepower, coal at $4 per ton. .$ 
Yearly cost per horsepower, coal at $3 per ton. .$ 



10 

7.00 

220.00 

242.00 

480.00 

178.00 

22.80 

923.00 

830.00 

730.00 

92.30 

83.00 

73.00 



12 

6.75 

204.00 

270.00 

560.00 

190.00 

24.80 

1,045.00 

940.00 

820.00 

87.00 

78.00 

68.00 



14 

8.50 

192.00 

295.00 

625.00 

202.00 

26.70 

1,149.00 

1,030.00 

900.00 

82.00 

74.00 

65.00 



15 

6.00 

186.00 

307.00 

670.00 

210.00 

27.60 

1,215.00 

1,100.00 

960.00 

80.00 

72.00 

63.00 



20 

5.50 

163.00 

360.00 

750.00 

238.00 

32.50 

1,380.00 

1,240.00 

1,080.00 

69.00 

62.00 

54.00 



Table C {Continued) 



1. Horsepower of engine 

2. Total coal per horsepower per hour, pounds 

3. Cost of plant per horsepower $ 

4. Fixed charges on plant at 11 per cent $ 

5. Cost of coal at $5 per long ton $ 

6. Attendance $ 

7. Oil, waste and supplies $ 

8. Total yearly cost, coal at $5 per ton. $ 

9. Total yearly cost, coal at $4 per ton $ 

10. Total yearly cost, coal at $3 per ton $ 

11. Yearly cost per horsepower, coal at $5 per ton. .$ 

12. Yearly cost per horsepower, coal at $4 per ton. .% 

13. Yearly cost per horsepower, coal at $3 per ton. .$ 



30 

5.25 

134.00 

440.00 

1,040.00 

297.00 

43.00 

1,720.00 

1,550.00 

1,360.00 

57.00 

51.00 

44.50 



40 

4.75 

120.00 

530.00 

1,310.00 

350.00 

53.00 

2,243.00 

2,020.00 

1,770.00 

56.00 

50.00 

43.50 



50 

4.25 

108.00 

590.00 

1,470.00 

405.00 

64.00 

2,529.00 

2,270.00 

2,010.00 

51.00 

46.00 

40.00 



75 

3. 

93, 

765. 

1,910. 

535. 

89. 

3,299. 

2,961. 

2,600. 

44. 

39. 

34. 



100 

3.50 

81.00 

890.00 

,420.00 

760.00 

114.00 

,094.00 

,700.00 

250.00 

41.00 

37.00 

32.50 



Yearly Cost of Steam Power, 308 Days, 10 Hr. per Day, Compound Condensing 

Engine 



Table D 



1. Horsepower of engine 

2. Total coal per horsepower-hour, pounds 

3. Cost of plant per horsepower. $ 

4. Fixed charges on plant at 11 per cent $ 

6. Cost of coal at $5 per long ton $ 

6. Attendance $ 

7. Oil, waste and supplies $ 

8. Total yearly cost, coal at $5 per ton $ 

9. Total yearly cost, coal at $4 per ton $ 

10. Total yearly cost,* coal at $3 per ton $ 

11. Yearly cost per horsepower, coal at $5 per ton $ 

12. Yearly cost per horsepower, coal at $4 per ton $ 

13. Yearly cost per horsepower, coal at $3 per ton $ 



100 

2.75 

105.00 

1,160.00 

1,910.00 

880.00 

143.00 

4,198.00 

3,780.00 

3,300.00 

42.20 

37.80 

33.20 



200 

2.45 

93.30 

2,060.00 

3,370.00 

1,220.00 

205.00 

6.948.00 

6,200.00 

5,400.00 

35.10 

31.50 

27.70 



300 

2.40 

86.40 

2,850.00 

5,100.00 

1,220.00 

240.00 

9,496.00 

8,550.00 

7,500.00 

31.50 

28.40 

25.00 



400 

2.35 

76.20 

3,350.00 

6,700.00 

1,760.00 

285.00 

12,171.00 

11,000.00 

9,700.00 

30.50 

27.00 

23.80 



J 



COST OF POWER 



313 



Table D {Continued) 



1. Horsepower of engine 

2. Total coal per horsepower-hour, pounds 

3. Cost of plant per horsepower $ 

4. Fixed charges on plant at 11 per cent .$ 

5. Cost of coal at $5 per long ton $ 

6. Attendance $ 

7. Oil, waste and supplies $ 

8. Total yearly cost, coal at $5 per ton. $ 

9. Total yearly cost, coal at $4 per ton . $ 

10. Total yearly cost, coal at $3 per ton $ 

11. Yearly cost per horsepower, coal at $5 per ton . .$ 

12. Yearly cost per horsepower, coal at $4 per ton . . $ 

13. Yearly cost per horsepower, coal at $3 per ton . .$ 



500 

2.30 

71.20 

3,920.00 

8,380.00 

1,930.00 

315.00 

14,596.00 

13,200.00 

11,500.00 

29.20 

26.10 

23.00 



600 

2.25 

67.30 

4,451.00 

9,650.00 

2,100.00 

350.00 

16,818.00 

15,700.00 

13,200.00 

27.70 

24.90 

21.90 



700 

2.20 

64.40 

4,952.00 

11,000.00 

2,650^.00 

385*00 

19,050.00 

17,200.00 

15,200.00 

27.30 

24.60 

21.50 



800 

2.16 

62.20 

5,492.00 

12,500.00 

2,700.00 

420.00 

21,674.00 

19,500.00 

17,100.00 

26.10 

23.50 

20.60 



Table D {Continued) 



1. Horsepower of engine 

2. Total coal per horsepower-hour, pounds 

3. Cost of plant per horsepower $ 

4. Fixed charges on plant at 11 per cent $ 

5. Cost of coal at $5 per long ton % 

6. Attendance $ 

7. Oil, waste and supplies $ 

8. Total yearly cost, coal at $5 per ton $ 

9. Total yearly cost, coal at $4 per ton $ 

10. Total yearly cost, coal at $3 per ton $ 

11. Yearly cost per horsepower, coal at $5 per ton...$ 

12. Yearly cost per horsepower, coal at $4 per ton...$ 

13. Yearly cost per horsepower, coal at $3 per ton...$ 



900 

2.10 

59.30 

5,910.00 

14,300.00 

2,930.00 

445.00 

23,644.00 

21,200.00 

18,500.00 

25.20 

22.60 

19.90 



1,000 

2.00 

55.70 

6,130.00 

14,500.00 

3,480.00 

470.00 

24,595.00 

22,200.00 

19,500.00 

24.50 

22.00 

19.40 



1,500 

1.80 

54.40 

9,000.00 

18,600.00 

4,400.00 

600.00 

35,100.00 

31,500.00 

27,500.00 

23.50 

20.30 

17.90 



2.000 

1.75 

53.20 

11,880.00 

24,200.00 

5,200.00 

685.00 

42,018.00 

37,800.00 

33,000.00 

21.00 

18.90 

16.60 



Another estimate is presented in Table 
pared by Mr. Webber in 1903. 



E." This table was pre- 



CosT OF Steam Power per Indicated Horsepower of 3,080 Hr. 

Table E 



1. Horsepower of plant 

2. Total plant per i.hp. including buildings 

3. Fixed charges, 14 per cent 

4. Coal per hp.-hr., lb 

5. Cost of coal at $4 

6. Attendance 

7. Oil, waste and supplies 

8. Total with $4 coal 

9. Total with $2 coal 



100 
$170.00 
23.80 

7.00 
38.50 
12.00 

2.40 



200 
$146.00 
24.40 

6.00 
35.70 
10.00 

2.00 



300 

$126.00 

17.65 

6.00 

33.00 

8.60 

1.72 



400 

$110.00 

15.40 

5.50 

32.00 

7.25 

1.45 



500 

$96.00 

13.45 

5.00 
27.50 

6.20 

1.24 



600 

$85.00 

11.90 

4.50 

24.70 

6.40 

1.08 



76.70 
57.45 



68.10 
50.25 



60.97 
44.47 



56.10 
40.10 



48.39 
34.64 



43.08 
30.73 



314 



ENGINEERING OF POWER PLANTS 



Table E (Continued) 



1. Horsepower of plant 

2. Total plant per i.hp. including buildings. 

3. Fixed charges, 14 per cent 

4. Coal per hp.-hr., lb 

5. Cost of coal at $4 

6. Attendance 

7. Oil, waste and supplies 

8. Total with $4 coal 

9. Total with $2 coal 



700 

$76.00 

10.65 

4.00 
22.00 

4.70 

0.94 



800 
$69.00 
9.65 
3.50 
19.20 
4.15 
0.83 



900 
$64.00 
8.95 
3.00 
16.50 
3.75 
0.75 



1,000 

$60.00 

8.40 

2.50 

13.75 
3.50 
0.70 



1,500 

$58.00 

8.12 

2.00 

11.00 
3.25 
0.65 



2,000 
$56.00 
7.85 
1.50 
8.25 
3.00 
0.60 



38.29 
27.29 



33.83 
24.23 



29.95 26.35 
21.75 19.47 

I 



23.02 
17.52 



19.75 
15.50 



per horsepower-year at the machine is a common assumption 
where steam is the motive power. 



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Fig. 211. — Cost of producing a horsepower-year of 3080 hours with simple non- 
condensing stationary engines with coal at $3.00, $4.00 and $5.00 per long ton. 



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Fig. 212. 



-Cost of producing a horsepower-year of 3080 hours with simple^condensing 
engines with coal at $3.00, $4.00 and $5.00 per long ton. 



The accompanying diagrams show other estimates of the yearly cost 
of producing steam power under various conditions and costs of coal when 



COST OF POWER 



315 



running 10 hr. a day for 6 days a week with fairly steady load. They are 
intended to show the expense of running under everyday conditions on 
such a plant as a prudent man would install with ordinary skill. 

Cost of 24-hr. power for 365 days per year is about 2.2 times the cost 
for 10-hr. power for 308 days. 



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Fig. 213.— Cost pf 
producing a horse- 
power-year of 3,080 
hours with com- 
pound condensing 

^. engines with coal at 

$3.00, $4.00 and 

^* $5.00 per long ton. 

S3 



100 300 



500 



700 900 1100 1300 1500 1700 1900 



Eorse-power 

Cost of 24-hr. power for variable load cannot be stated without know- 
ing all conditions. For varying load, usually add about 20 per cent, to 
coal consumption required for steady load. 

PROBLEMS 

73. Given: 

{a) 50,000 kw. turbine installation with maximum load of 35,000 kw. 

(6) 100,000 kw. turbine installation with maximum load of 70,000 kw. 

Coal $4.00 per net ton; 13,700 B.t.u. on dry basis. 

On the basis of the curves. Fig. 196, p. 293, determine probable annual operating 
cost and cost per kilowatt-hour for each plant if operating on a 40 per cent, load factor. 

Note. — With $3.00 coal the percentage distribution of station charges is 

Coal .* 80.0 Oil, waste, water, etc 2.5 

Labor 13 . Maintenance 4.5 

The following general data should be recorded: 

1. Installation, kw. 5. Kw.-hr. per yr. 8. B.t.u. per kw.-hr. 

2. Cost per kw, $ 6. Use factor, per cent. 9. Thermal eff., per cent. 

3. Total cost, $ 7. Load factor, per cent. 10. Coal per kw.-hr., lb. 

4. Max. load, kw. 

74. Given 10,000 kw. turbine installation with maximum load of 8,000 kw. 
using 13,500 B.t.u. coal at $6.50 per net ton. Determine the annual operating cost 
and cost per kw.-hr. for 100, 60, 35 and 20 per cent, load factor and plot curve show- 
ing cost per kw.-hr. versus load factor on a basis similar to that of Prob. 73. 

76. Given a 25,000 kw. turbine installation with maximum load of 20,000 kw. 
operating on a 35 per cent, load factor. 

Three grades of coal are under consideration: (a) 12,500 B.t.u. at $4.60 per ton; 
(6) 13,000 B.t.u. coal at $5.00 per ton; (c) 13,500 B.t.u. coal at $5.30 per ton. 

On a basis similar to that of Prob. 73 determine the annual operating cost and 
cost per kw.-hr. for each grade of fuel. 

76. Determine the annual operating cost and cost per kw.-hr. for the plants of 
Prob. 73 on the basis of "Percentage of Cost Distribution" on p. 295 and compare 
the results with those previously determined. 



CHAPTER XV 
HINTS ON STEAM PLANT OPERATION 

The following hints regarding the operation of steam power plants are 
given with the idea that they may be of service to the young engineer dur- 
ing the trials and tribulations that come with early responsibility. 

The operation or running of steam power plants with the accumulated 
experience of more than a century and a half might seem to most any one 
who has not been in the actual working to be a very simple problem, 
which throughout the last century at least had been standardized and 
was well understood. Indeed by talking to many operators whose duty 
it is to run steam plants, he would be sure that the last word had been 
said and that there was nothing to learn from further study. When one 
commences to investigate these plants from which such rose-colored re- 
ports are received and to note down and compare the figures, he will find 
discrepancies of a very serious nature, loop holes that are very wide indeed 
and he will soon find that his information is largely a matter of guesswork. 
If the investigator is an engineer, his scientific training will show him that 
the reported results are impossible and in searching around for the reasons 
he will fi;nd that his informant either is ignorant of the proper methods 
to apply and thus fooling himself with incorrect results, or he is simply 
hiding his own lack of knowledge by giving results he knows are not true. 

The man who reports a horsepower-hour on 1 lb. of coal or an evapora- 
tion of 14 lb. of water per pound of coal, is in the class with the man who 
sprinkles a small amount of some chemical on ashes and reports that he 
gets more heat from the ashes than from an equal amount of good coal. 
This same man is likely to tell you his furnace temperature is 3,200° and 
his flue gases 200°. 

The object of a power plant is to furnish power. When a power plant 
fulfills its purposes it must furnish power when it is wanted and in such 
quantities as wanted. It must be so run that power must be available 
whenever it is needed, that is, continuity of operation is essential and 
finally it must make and deliver power at as low a cost as is consistent 
with the circumstances of its design and location. 

To fulfill the above conditions the operator must study the plant as a 
whole and in detail with reference to the following: 

1. The plant must be studied to discover its strong points and weak- 
nesses, that is, how well the designer has attacked the problem. What 

316 



HINTS ON STEAM PLANT OPERATION 317 

has he forgotten or left out and how can the omissions be corrected? 
What particular parts cost more than the return from them warrants? 

2. Each piece of machinery must be gone over and a proper under- 
standing obtained of what may be expected of it. Is it fitted for the work 
it has to do? What would it cost to replace it with the best machine of 
its kind? Does it pay to run it? How should it be run to get the best 
results? 

3. Fuel, being the largest single item in station cost, should receive 
the most careful study. A study of the fuel supply of the district is most 
profitable and may show that you can obtain a better and cheaper supply 
of fuel without difficulty. 

Look into the methods of shipping and marketing the coal. It may 
be possible to buy the same coal in a different way to better advantage. 
How much water does the coal contain when delivered and what do you 
pay for the water? Look into the methods of storing, does the water 
evaporate or increase in the storage? Every pound of water evaporated 
from the coal in the furnace costs nearly as much to evaporate as if it 
were in the boiler and then wasted. Are the coal-handling arrange- 
ments bad or good? Sometimes conveyors cost more than coal handling 
with a horse and cart, or even a few sections of industrial railway. 

The percentage of refuse is important as well as the combustible in the 
ash. If the refuse is more than a few per cent, more than the ash content, 
something is wrong with the grates or with the firing. If the combustible 
in the ash is high, over 50 per cent., the firing is bad or the cleaning of 
the fires has not been done properly. Be careful that your samples are 
average samples. Many incorrect results are due to imperfect sampling. 
Watch the combustion and air supply. Carbonic-acid determinations 
from beyond the bridge- wall and in the flue should be regularly made. 
The apparatus is simple and cheap and when carefully made the results 
are valuable. The results will not be absolute, however, but comparable. 
For accurate results, very careful sampling and analysis are required and 
these are not usually obtainable except in plants of the maximum size 
where one man is trained to do only this work. It is quite difficult for 
anyone to duplicate results. 

4. Feed Water. — Is it pure or a good boiler water? A good boiler 
water is not necessarily pure. In fact pure water is too good a solvent 
and is not desirable. Is boiler compound needed? Do you buy patent 
medicine? The usual patented compounds are 50 cts. worth of lime and 
soda ash dissolved in a barrel of water and sold for 30 to 60 cts. per gallon. 
Learn what the scaling salts are and how they occur in the boiler water; 
and use the least amount of soda ash and lime that will soften the water. 
A little scale is not a bad thing. How much water do you blow off in 
the blowoff system? How much from the safety valves. What is the 



318 ENGINEERING OF POWER PLANTS 

leakage loss in the pipe system. Is there another source of feed water 
and how much does it cost? Are your water meters correct? Do they 
run fast on light loads? A known plant paid 40 per cent, more for water 
than it should, due to incorrect meters, so check them against weighing 
devices or a meter of the Venturi type once in a while. Are the steam 
pipes covered? What do you lose by condensation in the pipes? Are 
your drips thrown away or do they leak away? All clean drips should go 
to the boilers and there should be few dirty drips. 

5. Oil. — How do you lubricate the machinery in the plant? If you 
have an oil system, is it working well? How much oil do you use? How 
is it purchased? How do you check up the quality of the oil? Some 
operators buy on a kilowatt-hour basis. Other operators bay by the 
gallon or barrel. Do you use compounded oil? You will hear some 
operators claim that cylinder oil will not lubricate unless it contains a 
certain proportion of tallow — say 10 or 12 per cent. This is fallacious 
but it dies hard. Do you oil through the carrying action of the incoming 
steam or do you feed the oil drop by drop where it is needed and when it is 
needed? How much care is exercised in saving oil? 

Waste and Supplies. — How much waste do you use and how do you 
handle it? Will washable towels be better and cheaper than waste? 
Can you save oil that way? How do you look after packing gaskets and 
pump valves? Pump valves make good rubber heels. Do any of yours 
go that way? What small supplies do you keep and how are they issued 
and accounted for? 

6. Maintenance.— In this particular item the operating man may save 
or lose quite a little money. Boilers must be cleaned, engines must be 
overhauled, pumps must be packed and valves replaced. Condensers 
must be cleaned and tubes replaced. If oil is present in the condensate 
the steam side of condensers should be boiled out with a soda solution 
occasionally. The dust must be blown out of electrical machinery. 
Dust and dirt must be kept out of everything and heat should be saved 
everywhere. Regular schedules of overhauling help, and if the work can 
be done between times, with the regular force, a saving will be made. 
How do you handle extraordinary repairs? 

7. Labor. — Is your organization good or are you suffering from dead- 
wood, dry rot, soldiering or incompetency. How do you run your force — 
on the team work principle or individual plan ? Are your men ambitious 
for more work and responsibility or for more pay? Are they real me- 
chanics or just workmen? Do they take pride in their work? 

Finally. — Do you know the efficiency of your plant? Are you run- 
ning on 8 lb. of coal per kilowatt-hour, or on, say, 2.5 lb. or better yet, 
do you turn out a kilowatt-hour for 35,000 B.t.u. in the fuel or 50,000 
B.t.u., or even higher? Do you know your station water rate? Is it 



HINTS ON STEAM PLANT OPERATION 319 

20 lb. or 40 lb., and how accurately do you know it? What is your aver- 
age boiler efficiency over a year, water against coal? What is your bank- 
ing loss? Do you know your load factor and use factor? Can you by 
changing the use of your units improve your station economy? Which 
engine uses the most steam and which the least? Are the economy 
curves flat or deeply hollow? Do you know your costs? Who keeps 
them and are they kept accurately? Do you know what each piece of 
apparatus costs per year to keep it in good working operation? Costs 
are illusive and the operating man should look after them very carefully. 
How are your gages, thermometers and meters? Where and how were 
they rated? Do you keep standards to use for comparison? Are your 
valves tight? Do you keep the stems packed and what leakage do you 
have? Do you ever weigh your coal? How much does it lose in weight 
in the bunker? Do you wet down your coal? 



CHAPTER XVI 
POWER TRANSMISSION 

Shafting and Belting. — The oldest and most common method of trans- 
mitting power from the engine to the consumer is by means of shafting, 
gearing and belting. Until within 25 years hardly any other method was 
considered except in special cases. 

Chief Objection to this System. — The two chief objections to this 
system are its friction losses and its lack of adaptability. Experiments 
made by various engineers have shown losses between engine and machine 
in ordinary machine shops of from 50 to 60 per cent, of the total power 
transmitted by the engine. This loss is greatest in shops where large 
machines are employed, located at some distance from each other and it 
is here that other kinds of transmission can be used to advantage. Two 
incidental objections to shafting and belting are dirt and interference 
with proper lighting. These are objections of considerable importance 
in some shops as dirt and dust from the processes of manufacture are kept 
stirred up by the moving belts, often causing inconvenience to the work- 
men, and dark shops are not only objectionable from general standpoints 
but may lead to accidents. 

Cost of Shafting and Belting. — The cost of shafting, including the 
necessary hangers, couplings and pulleys will vary according to size be- 
tween $2 and $6 per linear foot. A rough rule which may be used in 
preliminary work is to allow SI per linear foot per inch of diameter. 

The cost of belts will vary from $5 to $50 for such widths and lengths 
as are used in ordinary shop practice. The discount on all kinds of belt- 
ing usually ranges from 50 to 70 per cent, of the list price. 

Rope Driving. — Ropes may take the place of belts in special cases, 
but cannot be said, in any sense, to have replaced them for ordinary use. 
Manila and cotton ropes are sometimes used for main drives to connect 
the engine with the head shaft, and less frequently for distributing the 
power to the different floors. 

It may be said in general that the first cost of ropes is less than of 
belts, but that they wear out much faster, are more difficult to splice, 
and are less efficient. They are sometimes valuable for carrying power 
at different angles. 

Wire ropes have been used to a considerable extent in the past for 
carrying power comparatively long distances, especially in places exposed 

320 



POWER TRANSMISSION 321 

to the weather, but electricity has almost entirely supplanted them. The 
initial cost of a wire-rope transmission for distances from 300 to 1,000 ft. 
is very small, and the running expense is no greater than that of electricity 
but the rope drive is much more limited in its application. 

Steam Transmission. — Where the area covered by an establishment 
is large it is often more economical to have a central boiler house and to 
transmit high-pressure steam to the various buildings, there to be used 
for both power and heating. The loss in transmission, although heavy, 
is probably much less than for shafting and belting if the pipes are of 
proper size and properly insulated. 

Efficiency of Transmission. — Rather extravagant claims have been 
made as to the advantage of electricity over shafting and belting in the 
matter of efficiency. Experiments on several group installations in 
machine shops have shown a loss of from 40 to 60 per cent, of the total 
power of the .engine before reaching the machine, as previously pointed 
out. These losses are due partly to the shafting and belting and 
would be reduced with independent motors. Direct tests on 16 large 
machines driven by independent motors in a locomotive works showed 
an average of 8.85 hp. for the machine and its work and 2.35 hp. for the 
power consumed by the motor and countershaft. This means an effi- 
ciency of less than 80 per cent, for the motors, not counting the losses in 
the generator and transmission lines. On the other hand, it may be 
said that although the friction losses in shafting and belting remain nearly 
constant at all loads, the electrical losses will diminish as the load falls off. 

The following sections relating to '^ Electric Drive Versus Shafting 
and Belting" have been thoroughly revised and brought down to date 
by C. E. Clewell, Assistant Professor of Electrical Engineering at the 
University of Pennsylvania, whose articles in American Machinist 
(1914-15) relating to this subject are well known. 

Electric Drive Versus Shafting and Belting. — The main advantages of 
the electric drive are included under the heads of ^'Location of Machines,'' 
''Head Room," ''Centrahzed Power," ''Reliability," and the "Ability to 
Study Machine Performance."^ 

Flexibility in the location of machinery with electric drive has come 
to be an acknowledged advantage in machine-shop work and particularly 
in the use of portable tools. The clear head room resulting from the use 
of individual motor-driven machines and the eliminating of overhead 
belting, adapts manufacturing spaces to improved lighting and venti- 
lating conditions, and to more effective crane service, since the interfer- 
ence of overhead belts often dictates just what portions of a shop may 
be served by the crane and which may not. Furthermore, a centralized 

1 "American Handbook for Electrical Engineers," John Wiley and Sons, New York,, 
p. 972. 



322 ENGINEERING OF POWER PLANTS 

power station is made possible through the medium of electric power 
distribution, thus making changes and extensions of the plant practically- 
independent of the power supply. Under reliabihty, it follows that the 
breakdown of a single motor which is individually connected to its own 
machine tool, affects the operation of that machine only, whereas a break- 
down in the belting or shafting of a line-shaft drive, often causes interrup- 
tion for a larger group of machinery. 

The study of machine performance which is a valuable accompani- 
ment to improved production methods, and to the application of so-called 
''scientific management" to machinery practice, has practically been 
made possible for the first time, through the use of the recording and 
graphic electric meters which may be used in conjunction with indi- 
vidually motor-driven machinery. This feature of electric drive is be- 
ginning to be recognized as one of its most important advantages. 

Methods of Motor Drive. — These may be classified as ii^dividual and 
as group drives. In the former, each machine is fitted with its own motor, 
either driven directly or through a countershaft, and there is an entire 
absence of overhead belts. This system is particularly applicable to 
shops having large machines located some distance apart and perhaps 
varying in character. It is necessary, however, in such cases to control 
the speed of the machine directly through the speed control of the motor, 
and this may be done by any one of the various methods of motor speed 
control. Ranges of speeds of 4 to 1 are common, but in some special 
cases speed ranges as high as 10 to 1 are available for motor drive. 

In the group method, several machines are arranged in a group and 
are driven by a short line shaft which is driven in turn by a motor. This 
makes it possible to use a constant-speed motor because the speed adjust- 
ments of the machine tool are effected in the ordinary manner through 
the medium of cone pulleys or gears. The size of the motor may also be 
smaller than that of the motors used for the corresponding machine tools 
with the method of individual motor drive, on account of the diversity 
factor of the group of machines. 

On the other hand, with the group method of driving, the overhead 
belts are only partially done away with, and there is not that freedom of 
arrangement which makes the individual method of driving so desirable. 
It is also necessary in this connection to distinguish between the use of 
direct- and alternating-current motors. In general, individual motor 
drives necessitate direct-current motors, because of their adaptability 
to flexible speed control, while in the group method either direct- or 
alternating-current motors may be used since the motor under this con- 
dition may usually be of the constant-speed type. 

The choice of direct or alternating current for machine-shop drives 
depends also to some extent upon whether there is a possibility or likeli- 

21 



POWER TRANSMISSION 323 

hood of throwing over, at certain times, to an outside power company's 
circuits. If the ready-to-serve charge is not too great, the alternating- 
current distribution from this one standpoint may be best, because the 
alternating current which is usually employed by the large central power 
stations, could thus be relied upon at certain times. 

In the case of an individual shop power plant in which the amount of 
power required by the shop is large and there is no public service corpora- 
tion to rely upon in the neighborhood, the question of direct or alternating 
current is partly dependent on the area covered by the plant, and partly 
dependent on the need for adjustable-speed motors. Alternating current 
is satisfactory both for small and for large plants from the viewpoint of 
distribution, but from this same viewpoint, direct current is hardly suit- 
able for a plant extending over a. considerable area, because of the large 
drop in voltage due to the long lines required and the relatively low supply 
voltages usually employed with direct-current systems of distribution. 
Adjustable-speed motors, however, are mainly of the direct-current type, 
and where their use is essential, it may be found desirable to employ 
alternating current for the main distribution circuits, and to transform 
from alternating to direct current by rotary converters or motor-generator 
sets, to meet the need of a source of direct current for motors of this type. 
In some plants, therefore, circuits of both types will be found, those of 
the alternating-current type being depended upon for lighting, and con- 
stant-speed motors, and those of the direct-current type supplying the 
adjustable-speed motors and sometimes certain electric lamps which are 
operative only on direct-current circuits. 

Some years ago a great deal of discussion took place about the possi- 
bility of adjustable-speed motors for the various forms of machine-tool 
drive. Motors of this type are now available and are widely used. 
Machine-tool builders, who in the past have found it necessary to design 
their tools so as to get speed changes mechanically, now in many cases 
find it desirable to adapt the design of their machines for operation by 
individual electric motors. 

The amount of power drawn for any given tool varies usually over a 
wide range, and a motor should be put on an individual tool which can 
take care of the largest load that the tool is apt to require, although its 
rated capacity need not be determined by this maximum demand on 
account of the liberal overloads which modern motors can develop for 
short intervals without excessive heating. In general, if a number of 
tools are grouped together, a motor that is appreciably smaller than the 
sum of the individual horsepower capacities required on the different 
tools may be installed. This is illustrated by the fact that even in the 
case of the group drive, the actual power drawn from the generator may 
be less than the total rated capacity of the motors connected to the gener- 



324 ENGINEERING OF POWER PLANTS 

ator. It must be remembered, however, that the power required to drive 
a machine tool is very small in proportion to the total cost of production 
chargeable to that tool, and hence other advantages of the individual 
motor drive may entirely offset the small gain in reduced motor size when 
the group method is employed in contrast to the individual method of 
drive. 

In the installation of all motors, because of low efficiency at low loads, 
care should be taken that motors not too large for the work are chosen. 
With alternating-current motors, the fractional loads are also accom- 
panied by low power factor; hence for this additional reason it is better 
to operate an alternating-current motor at or near its full rated capacity 
rather than at a load much below normal for a large part of its operation. 

To summarize the matter of group versus individual methods of 
drive, it may be stated that there is still much difference of opinion regard- 
ing their relative advantages, although these differences of opinion are 
not so marked as was the case 10 years ago. Both methods are quite 
widely used, and each individual case requires careful study before an 
intelligent decision can be reached as to the actual merits of each method. 
In many cases both methods of driving will be found in the same plant. 

Three items ^ stand out as most important in this question: (a) the 
influence of the character of the load; (b) the influence of speed; and (c) 
the influence of relative cost. Under (a) there is a general acceptance of 
the conclusion that where machines are operated intermittently, the 
method of individual drive is to be preferred. With the group method, 
the total load is made up partly of friction and other mechanical losses 
which go on continuously, and partly by the demand of the machine 
tools themselves when working. If, therefore, the load factor of the 
machines is low, the friction losses form a larger percentage of the total 
power consumed, and the *group system thus becomes less efficient than 
where the machine load factor is high. 

Under (b) the wide range and fine gradations of speed with an indi- 
vidual adjustable-speed motor give it a decided advantage in the matter 
of speeds over the group or line-shaft drive. The modern interpole, ad- 
justable-speed motor possesses excellent commutation characteristics 
both at heavy and at light loads for a wide range of speeds, thus overcom- 
ing one of the larger difficulties in earlier types. Under (c) it may be said 
that the choice between individual and group drives is essentially one of 
relative cost. While the first cost of the motor equipment for individual 
driving is greater than the cost of the motor equipment for group driving, 
the economic returns through increased production by the use of indi- 
vidual motors may actually offset the higher first cost in a relatively short 

1 "American Handbook for Electrical Engineers," John Wiley and Sons, New 
York, p. 973. 



POWER TRANSMISSION 325 

time interval. Moreover, what may be termed secondary advantages, 
such as a more open shop space, better illumination and ventilation, and 
improved crane service, all form additional advantages in favor of the 
individual drive. 

Sizes of Motors Recommended to Drive Machine Tools. — The average 
load factor for motors driving lathes is from 10 to 25 per cent. On some 
special machines, as driving-wheel and car-wheel lathes, the cuts are all 
heavy, which increases the average load factor to from 30 to 40 per cent. 

For extension boring mills, 5-hp. motors are used to move the housings 
on from 10-ft. to 16-ft. mills, T^-hp. for from 14-ft. to 20-ft. mills and 
10-hp. for from 16-ft. to 24-ft. mills. The load factor of the driving motor 
on boring mills averages from 10 to 25 per cent. 

The load factor of motor-driven drills is about 40 per cent., when the 
larger drills applicable thereto are used. If the smaller drills are used, 
the load factor averages 25 per cent, and lower. 

For the average milling operations the load factor averages from 10 to 
25 per cent. On slab-milling machines where large quantities of metal 
are renewed it will average from 30 to 40 per cent. 

On planers the load factor averages between 15 and 20 per cent. The 
motor must be large enough to reverse the bed quickly, yet this peak 
load occurs for such short intervals that it does not increase the average 
load per cycle very much. 

The work done on shapers is of a varying character. With light work 
the load factor will not exceed 15 to 20 per cent.; with heavy work, the 
load factor will be as high as 40 per cent. 

Selection of Motors and Speed Requirements for Machine Service. — 
The selection of the proper motor for given service requirements necessi- 
tates a careful study into the characteristics of the work to be performed 
by the machine tool. Both power and speed requirements vary widely in 
different tools, and a motor well adapted to one class of work may be 
unsuited to another. Expett advice should be secured in such a problem 
until the factors involved are thoroughly understood and the characteristics 
of the various types of motors on the market are mastered in their relation 
to the power and speed conditions to be supplied for given machines. 

The importance of speed is at once realized when one considers that 
production depends to a great extent on the use of the most economical 
cutting speed for given operations. The 4 to 1 adjustable-speed motor 
now commonly employed in machine-shop work will be found to meet 
most conditions. It is recommended^ that given machine tools be re- 
stricted to a certain range of diameters of work and thus make possible 
a close speed adjustment within this range, rather than to work a maxi- 
mum range of diameters on a given tool with less refinements in the speed 

' Westinghouse practice. 



326 ENGINEERING OF POWER PLANTS 

adjustment. Useful charts are available from the larger electrical manu- 
facturers by means of which the horsepower requirements for given depths 
of cut, cutting speeds and feed, may be determined conveniently. Simi- 
larly, charts are available from which the relation between feeds, cutting 
speeds, diameters of work, and spindle speeds may be determined con- 
veniently. The following table^ is also useful in this general connection: 

Horsepower per cubic 
Metal foot of metal per 

minute 

Cast iron 0.3 to 0.5 

Wrought iron 0.6 

Machinery steel 0.6 

Steel, 50 carbon and harder 1 . to 1 . 25 

Brass and similar alloys . 2 to . 25 

For drills, the cubic inches of metal removed per miimte are found by the 
formula : 

Q = 0.7854 X d^f 

where d is the diameter of the drill in inches and / the feed in inches per 
minute. The constants for drills are approximately double those given 
in the previous table. 

Cost of a Horsepower at the Machine. — The cost of power trans- 
mitted electrically to the consumer will depend on the original cost at 
the engine or water power. Power transmitted from a large waterfall 
by electricity frequently sells for $25 per horsepower-year for short dis- 
tance transmission. (It is reported that Niagara power sells from $12 to 
$24 per horsepower-year.) 

Mr. W. C. Webber estimates the total cost at the machine of electrical 
transmission in shops as follows, allowing for interest and depreciation 
and including repairs, attendance, etc. : 

Per horsepower-year of 3,080 hr ,. $52 

Per horsepower-year of 7,392 hr , 57 

Per horsepower-year of 8,760 hr 66 

These are computed on a basis of 100 hp. produced at the engine for $35 
per horsepower-year at 3,080 hr. 

One authority states that with coal at $3 per ton a simple non-con- 
densing, high-speed engine will produce 500 hp. at a cost of $36 per horse- 
power-year of 3,080 hr., while a triple-expansion condensing engine will 
furnish the same power for $24. 

The probable costs in an electric system for furnishing power to a 
machine shop might be summarized as follows: 

1 Westinghouse Electric and Manufacturing Co. The table refers to lathes, 
planers, etc., when round-nose tools are used. 



POWER TRANSMISSION 327 

Cents per kilowatt-hour 

Coal at $3.50 per ton 0.5 

Labor 0.4 

General expenses 0.2 

Fixed charge 0.4 

Total 1.5 

This does not allow for the cost or losses of distribution, but represents 
the cost at the switchboard, and corresponds very nearly to $35 per horse- 
power-year of 3,080 hr. 

The following data has been compiled by the Bullock Electric Manu- 
facturing Co. for the cost of power compared with output of the factory 
for different systems of transmission: 

(a) Ordinary belting and shafting 1 . 7 to 2 . per cent. 

(6) Electric group drive . 8 to 1 . per cent. 

(c) Individual motor drive 0.4 per cent. 

It is evident that there is a marked saving in power through the use of 
individual motor drive, but it is also apparent that in most factories the 
important factor is increase in output, and if one system of power effects 
an increase of even 50 per cent, in the power consumption, this increase 
is relatively a small factor in the total cost of production. In this con- 
nection, it may be stated that there is abundant testimony that the in- 
stallation of individual motor drive in large shops has effected from 20 
to 40 per cent, increase in the output for given machine tools, and an 
equal or even greater economy in room. 

Through the cooperation of Professor H. B. Dates the following notes 
relating to electrical machinery are given: 

Direct Cttrrent versus Alternating Current. — For equal low voltages 
usually found in the small machine shop of say 250 volts, both systems 
require the same amount of copper in general terms in the matter of dis- 
tribution about the buildings of the plant. If the three-wire system is 
used with the direct-current and the two- wire system with the alternating- 
current, the advantage is in favor of the direct-current system. The 
advantage of the alternating-current system lies in the flexible method 
of transformation from low to high voltages and vice versa by means of the 
transformer, thus permitting the use of high voltage for the power trans- 
mission at low current and consequently low line losses and low copper 
costs. Direct current is usually generated at comparatively low voltage 
and it cannot readily be transformed from one voltage to another as with 
the alternating current. Direct-current motors, however, are essential 
where adjustable-speed service is a requirement. Incandescent lamps 
may be operated on either direct- or alternating-current circuits. Lamps 
of the 110-volt class, however, are better than those designed for opera- 
tion on 220-volt circuits. 



328 ENGINEERING OF POWER PLANTS 

High voltages, which are desirable for economy in the transmission 
of power over long distances, are more or less out of place in most manu- 
facturing plants, and consequently in the smaller plants where the dis- 
tances to be covered are relatively small, direct current is used. With 
a low-voltage direct-current system, 110 or 220 volts, there are no trans- 
formers to install and maintain, there is no danger from very high volt- 
ages, and the system as a whole is characterized by simplicity both in 
design and operation. As extensions are made to such a plant, however, 
the difficulties in power transmission become greater due to the heavy 
copper losses at low voltage, and it may be desirable to use alternating 
current at a higher voltage. From these circuits, lamps and constant- 
speed motors may be supplied, and where adjustable-speed direct-current 
motors must be used, special direct-current circuits may be employed, 
the transformation from alternating to direct current being effected by 
the rotary converter (also known as the synchronous converter) or by a 
motor-generator set. 

Direct-current Motors, Types and Where Used. — Shunt motors 
possess good starting torque and favorable operating characteristics for 
many operations. Their speed regulation is usually very good. They 
may be used where the load at starting is fairly high and where practically 
constant speed is desired at all loads, i.e., for line shafting, group drives, 
and for many machine tools. 

Series motors are used only where they can be geared or securely 
coupled to their load, to prevent the excessive speeds which result when 
the load on a series motor is thrown off. They are adapted for heavy 
starting duty where variations in speed are not objectionable. In such 
motors the speed varies approximately inversely as the square of the load. 
Series motors are adapted to street-car service, to cranes, heists, fans and 
similar loads. 

Compound motors, cumulatively wound, have characteristics which 
depend upon the relative strength of shunt and series field coils. These 
motors have operating features which result from the combined effects 
of series and shunt windings, so that in a measure the action is partly 
like that of a shunt motor and partly Uke that of a series motor. Cumu- 
lative-wound compound motors possess a good starting torque, but are 
apt to have poorer speed regulation, that is, a greater drop in speed with 
increases in load, than in the case of the straight shunt motor. 

Compound-wound motors of the cumulative type are sometimes used 
on loads where fairly large torque is required at one portion in each cycle 
and where the load is relatively light for the rest of the cycle. They are 
used quite extensively for elevator work, heavy planers, and for similar 
loads. It should be noted that a portion of the torque in this motor is 
due to its series-motor characteristics, but when the speed increases, the 



POWER TRANSMISSION 329 

field flux does not tend to decrease therewith as in the series motor, be- 
cause the current in the shunt circuit remains practically constant. The 
employment of the shunt field in addition to a series field thus prevents 
the speed from exceeding safe limits at low loads. 

Interpole or Commutating-pole Motors. — This type has come into 
very wide use during recent years for adjustable-speed machine-shop 
service. The interpoles render commutation practically perfect under 
wide ranges of speeds and loads. Adjustable-speed motors with wide 
speed ranges cost more than constant-speed motors of the same horse- 
power rating. 

Temperature rise, rather than commutation, is the limiting factor in 
the output which can be supplied by a given motor. For constant-speed 
service the use of interpoles is not as essential as in the adjustable-speed 
service. In constant-speed service, however, where the load is subject 
to rapid and violent fluctuations and where very large overloads must be 
carried, the design should be such as to take care of the main heating 
effects, while interpoles may be employed to maintain perfect commuta- 
tion under severe load conditions. Therefore, for intermittent constant- 
speed service, the interpole motor is more desirable than the motor of 
usual design. 

In direct-current railway service the use of interpoles enables motors 
to withstand large loads for short periods, or, where artificial ventilation 
is used, to operate continuously at overloads without excessive sparking 
as a limiting factor. This statement also applies in a general way to 
series motors used for mill purposes. 

Shunt motors, when used for adjustable-speed service, have their 
performance greatly improved with interpoles, and it is possible to reverse 
a 5-hp. shunt motor when interpoles are used, under full-load conditions, 
without sparking. This is not possible with ordinary shunt motors. 

The interpole motor is simple in construction, requires but two service 
wires, works at maximum voltage, that is, from circuits of normal voltage, 
may have its speed control accomplished by the insertion of a rheostat 
in the field circuit in the ordinary manner, and operates throughout a 
large speed range at almost constant efficiency. Direct-current motors 
of the interpole type, therefore, especially lend themselves to machine- 
tool work where adjustable speed is required and where good speed regu- 
lation under fixed positions of the controller is necessary. They are 
successfully used from about K2 to 1,500 hp. and larger in mill and shop 
work. 

Alternating-current Motors. — Polyphase, that is, two- and three- 
phase induction motors are chiefly used on alternating-current circuits 
in the shop. Sometimes the single-phase induction motor is used in the 



330 ENGINEERING OF POWER PLANTS 

smaller sizes but for power work the polyphase type is nearly always 
employed. 

The induction motor is inherently a constant-speed motor and it is 
largely used as such. If the rotor of an induction motor is of the phase- 
wound type (rather than the squirrel-cage type) with the use of auxiliary 
resistances in the rotor circuit it can be made to operate as an adjustable- 
speed motor but to a very limited extent and at the expense of efficiency 
and good speed regulation under various loads. Probably the greatest 
usefulness of the induction motor, therefore, is as a constant-speed 
machine. In this form, it is simple and rugged in construction, has no 
commutator or brushes, and when completely enclosed requires a mini- 
mum of attendance. It has a wide application in certain kinds of mill 
work, for example, for cement and paper mills and in reduction works. 
In addition to the use of auxiliary resistance in the wound rotor circuit 
for obtaining speed changes as well as greater torque at starting, speed 
changes may also be produced to a limited extent in the induction motor 
by the '^potential," *' change of poles," '^ change of frequency," or 
'' cascade control" methods^ 

Where power is purchased from a central power station, the supply 
is most commonly alternating current. In such a case the induction 
motor will be satisfactory for most constant-speed work, and should be 
employed unless adjustable-speed motors are essential, thus calling for 
direct-current circuits. Since the usual sources of alternating-current 
supply are at relatively high voltages and since it is customary to utilize 
the power at relatively low voltages, the use of a transformer is necessary 
for stepping down the voltage. 

Very large induction motors are often run at voltages as high as 6,600 
volts, i.e., direct from the line without the interposition of transformers. 

The steel plant at Gary, Ind., successfully uses induction motors of 
6,000 hp. on the rolls. The motors are equipped with heavy flywheels 
and the design is such that the peak loads are taken by the flywheels. 

Generators. — Direct-current generators have reached a high stage of 
development in multipolar types and at lower speeds than formerly. 
They have been improved mechanically and there has been a transition 
from the belted to the direct-connected type. 

The belted type is higher speed than the direct-connected, is lighter 
in weight for given output, and consequently is lower in first cost. 

In the direct-connected type there is a saving in floor space, no belting 
with its dust and dirt, less noise and a saving of one bearing in moder- 
ate-sized machines as the generator is mounted on an extension of the 
engine shaft. 

In buying a direct-connected set, if the engine is bought from one 

^ For information on these methods see "American Handbook for Electrical Engi- 
neers," John Wiley & Sons, New York, pp. 1009-1011, 



POWER TRANSMISSION 331 

manufacturer and the generator from another, it is customary for the 
engine manufacturer to furnish the shaft. Details are furnished the gen- 
erator manufacturer and the shaft is sent to him. He then mounts the 
rotating member of the generator upon it. 

In modern practice only the smaller units are belt-driven. 

Alternating-current generators in the earlier designs were of the single- 
phase type, with high frequency, 125 to 133 cycles (now obsolete), and 
were usually of small capacity and designed for belted operation. 

Rapid development has been made in polyphase types both two- and 
three-phase, 60 and 25 cycles. 

Single-phase motors are not good in large sizes, owing to the fact 
that they are not self -starting, except by the use of special starting devices 
which in general do not afford good starting torque. 

Polyphase systems are dictated from power considerations since the 
polyphase motor is self -starting, and gives highly satisfactory service. 

The polyphase generator is superior to the single-phase in performance 
(regulation), cost and weight. 

Distribution is cheaper with three-phase than with single-phase. 

Single-phase systems are limited to small plants where the motor load 
is very light. A single-phase machine of 200-kw. capacity is very rare. 

Lighting and power systems may both be fed from the same polyphase 
lines, although lighting circuits should always be kept separate from the 
power circuits so as to eliminate voltage fluctuations and the consequent 
flicker and unsteadiness usually found when lamps and motors are sup- 
plied from the same circuit. 

A three-phase generator may be loaded to 58 per cent, of its total 
three-phase output when operated single-phase. There seems to be little 
reason for installing single-phase generators at the present time. 

Three-phase systems are usually preferable to two-phase systems and 
are most generally used today. Where two-phase current is desired for 
special uses it may be obtained from the three-phase circuit by the Scott 
transformer connection. 

Three-phase systems are always used for economical transmission. 

Alternating-current generators have voltages which are seldom as low 
as 440 volts; 2,300 volts is common. Where transmission is over a fairly 
short distance, from say 6 to 15 miles, generators may and usually do 
operate at line voltages of 6,600, 11,000 or 13,200 volts. Generators are 
thus built to develop voltages as high as 13,200 volts. 

Where transformers have been used to step up to higher line voltages 
for longer transmission distances, generators are commonly built at one 
of the following voltages: 2,300, 4,000, 6,600, 11,000, or 13,200. Alter- 
nating-current generators driven by steam turbines are now in operation 
with capacities as high as 35,000 kv.a. 



332 ENGINEERING OF POWER PLANTS 

Standard voltage for alternating-current circuits may be listed as 
follows: 110, 220, 440, 2,300, 6,600, 11,000, 13,200, 22,000, 33,000, 66,000, 
90,000, 110,000 and 150,000. Standard frequencies in this country are 
25 and 60 cycles per second with some 40-cycle installations. Arc lamps 
do not in general operate satisfactorily on circuits with a frequency 
below about 40 cycles. Incandescent lamps may be operated on 25-cycle 
circuits but with slightly less satisfactory results than with higher 
frequencies. 

Twenty-five-cycle current is preferable for motors, especially so for 
rotary converters and synchronous motors. It is also preferable for 
transmission on account of better line regulation. 

For general purposes as mixed lighting and power, 60-cycle current is 
used; or power purposes, 25-cycle current. 

Exciters for Alternators. — All alternating-current generators require 
direct current for excitation of fields. In large stations exciters are 
direct-connected to prime movers. In small installations they are 
frequently direct-connected to or belted to the alternator itself. 

Exciter plant must be absolutely reliable; hence a reserve of good 
capacity is required either in the form of additional units or in storage 
battery or both. 

Capacity Required in Exciters. — For medium speed, small-sized alter- 
nators, the exciter capacity is usually about 2.5 per cent, of that of the 
generator. In large steam-turbine units, high-speed, it is about 0.5 per 
cent. 

Ratings by Output. — All electrical apparatus should be rated by out- 
put and not by input. Generators, transformers, etc., should be rated 
by electrical output; motors, by mechanical output. 

Rating in Kilowatts. — Electrical power should be expressed in kilo- 
watts except when otherwise specified. 

Apparent Power, Kilovolt -amperes. — Apparent power in alternating- 
current circuits should be expressed in kilovolt-amperes as distinguished 
from real power in kilowatts. When the power factor is 100 per cent., 
the apparent power in kilovolt-amperes is equal to the kilowatts. 

Rated (Full-load) Current. — Is that current which with the rated 
terminal voltage gives the rated kilowatts or the rated kilovolt-amperes. 

Determination of Rated Current. — If P be the rating or true watts, 
assuming a power factor of unity, and E be the full-load terminal voltage, 
then rated current per terminal is : I = P/E in a direct-current machine 
or single-phase alternating-current generator. 

I = 0.58 X P/E in a three-phase alternating-current generator. / = 
0.50 X P/E in a two-phase alternating-current generator. If the power 
factor is other than unity, divide P by the power factor in per cent. 

Temperature Rise. — Under regular service conditions the temperature 



POWER TRANSMISSION 333 

should never be allowed to remain at a point which will result in perma- 
nent deterioration of the insulating material in the machine. 

It has been recommended^ that the following temperature rises re- 
ferred to room temperatures of 40°C. be never exceeded. (These are to 
be considered as maximum permissible temperature rises above 40°C. 
allowable; manufacturers should keep within these limits.) 

A. For cotton, silk, paper and similar materials, when so treated or impregnated as 
to increase the thermal Hmit, or when permanently immersed in oil, also enameled 
wire, 65°0. 

B. Mica, asbestos and other materials capable of resisting high temperatures, in 
which any class A material or binder is used for structural purposes only, and may 
be destroyed without impairing the insulating or mechanical qualities of the insula- 
tion, 85°C. 

C. Fireproof and refractory materials such as pure mica, porcelain, quartz, etc. 
no limit specified. 

Effects of Semi and Totally Enclosing Direct-current Motors. — With 

semi-enclosing, at normal temperature rise, the output is reduced. Fully- 
enclosing the motor reduces the rating still more below normal. Forced 
cooling raises the rating above normal. 

The general plan today is to operate one large central station and 
locate at various centers substations for local distribution. 

Irrespective of the form in which power is distributed, i.e., alternating 
current or direct current, the power is delivered to the substations from 
the main generating plant (alternating-current plant usually now) as 
three-phase, high-voltage and at the substation it is transformed either 
as regards e.m.f. or in addition from alternating to direct current ac- 
cording to the demand. 

For transmission a general figure of about 1,000 volts per mile may 
be used up to present limits of say 150,000 volts. 

1 See Standardization Rules of the American Institute of Electrical Engineers, 
edition of July 1, 1915. 



CHAPTER XVII 
DISTRICT HEATING 

Although the discussion of heating from central stations belongs 
primarily to courses on ''Heating and Ventilation," yet the transmis- 
sion of steam or hot water for this purpose is so closely allied with 
power generation that brief notes relating to this subject are added. The 
material presented is largely from the published^ data of Bushnell and 
Orr, and Gifford. 

There are two distinct systems of central heating, steam and hot water. 
Central heating as a byproduct has proved very attractive financially in 
many cases and either system, steam or water, should give excellent 
results if properly installed and managed and, for this reason, both sys- 
tems have become popular and have increased in number. 

Central heating as a utility is very similar to any other business. 
To be successful the heat must be manufactured as economically as possi- 
ble. It must be marketed economically and it must be made attractive 
both as to price and quality of service. 

Advantages to the Public. — 1. Comfort, even heat, always ready. 

2. Cleanliness around the premises. 

3. Reduction of labor. 

4. Reduction of cartage through city streets. 

5. Reduction of smoke nuisance. 

6. Safety. 

The Bjrproduct Plant. — The thermal efficiency of an electric plant is 
very low. Even after the steam is generated 70 to 90 per cent, of the 
heat is exhausted after passing through the prime mover. If this steam is 
exhausted to the atmosphere, the waste is enormous. If it is condensed, 
the heat in the exhaust steam is transmitted to the cooling water and 
liberated, either through the cooling tower or pond. At any rate, it is 
wasted, but, of course, not so much of it is wasted in the condensing plant. 
However, when an electric plant is so located that it can serve a good 
heating territory, it can make a kilowatt of electric energy for considerably 
less in conjunction with a heating plant than it can by running alone con- 
densing. It is a problem that must be worked out for each situation, 
but, as a general rule, the revenue from the heat sales will more than pay 

^ District Heating," Bushnell and Orr, Heating and Ventilating Magazine Co., 
N. Y. 

"Central Station Heating," Gifford, Heating and Ventilating Magazine Co., 
N. Y. 

334 



DISTRICT HEATING 335 

the coal bills after deducting from the heat income interest, maintenance 
and depreciation on the heating investment. 

Combining these two utilities then increases the net earnings of each. 
It increases the load factor of the boiler plant and causes it to operate 
more economically because of the better load conditions. It increases 
the heat units utilized and sold. It should not increase the labor cost 
as the same crew can handle both. It increases the electrical output 
because it does away with isolated electric and power plants. 

If the central plant can serve its patrons with heat, light and power, 
it is not half so difficult to get this business because, as a rule, the owners 
of the isolated plants can buy these commodities from the central plant 
for less money than they can make them themselves, but if heat is not 
furnished by the central plant they cannot afford to buy electricity and 
make their own heat, as they heat with the exhaust steam from their 
own plant which, they naturally figure, costs them practically nothing. 
This kind of business materially helps the electric plant because it in- 
creases its load and its net earnings. 

In general, the combining of these two utilities is very satisfactory 
and advantageous to. both. 

Methods of Selling Heat. — The methods of charging for heat may be 
divided into five classes: 

{A) Flat rates per square foot of radiation for hot-water systems. 

{B) Flat rates per square foot of radiation for steam-heating systems. 

(C) Flat rates per square foot of radiation, theoretically required ac- 
cording to the company's formulae. 

iP) Flat rate per year based on estimates of service requirements, or 
else based on estimate of what the customer would be willing to pay. 

{E) Schedule prices based on the amount of steam used as shown by 
either steam or condensation meters. 

Class "A" — ^Flat Rates for Hot-water Heating. — It can readily be 
seen that the price for heating during the heating season in the Southern 
States ought to be very much lower than in a State like Maine or Minne- 
sota. The majority of heating plants are located in the Northern States 
and the variation in price would be approximately from 15 to 25 cts. per 
square foot. of radiation, with 20 cts. as an average price in the neighbor- 
hood of Chicago, 111. 

Class "B" — ^Flat Rates for Steam Heating. — The rate for steam radia- 
tion is about 50 per cent, higher than that for hot-water radiation, the 
price varying from about 25 to 35 cts. per square foot of radiation for 
districts having a temperature condition approximately like that of Chi- 
cago, 111. The difference in rates between steam and hot-water radiation 
is due to the fact that steam radiation usually transmits about 50 per 
cent, more heat per square foot of radiating surface than is transmitted 
by hot- water radiation. 



336 



ENGINEERING OF POWER PLANTS 



Class "C" — Contracts Based on Theoretical Required Radiation.— 

Contracts are also based on a flat rate dependent on the amount of radia- 
tion required as determined by the formulae of the company. In this 
form of contract the price is governed not only by the amount of radiation 
installed, which is the minimum, but also by the theoretical radiation 
required to heat the building, according to the formulae adopted by the 
company. 

Class "D" — ^Flat Contract. — Unfortunately with a great many heating 
companies many of the contracts are based on a flat price, which has been 
arrived at in a manner similar to that of a peddler in selling his wares. 
In other words, neither the buyer nor the seller has a very correct idea 
of what the service is worth, but after due discussion arrive at a price 
which becomes the basis of their agreement. There is always a tempta- 
tion on the part of customers toward wastefulness where the service is 
based on a flat price per year and all formulae used in figuring such con- 
tracts should take account of this fact. The average result in New York 
and Chicago shows that the consumer will use about 25 per cent, more 
steam when operating under flat-rate contracts, than when operating on 
a meter basis. 

Class "E'* — Contracts Based on Meter Readings. — In Class ''E" the 
contracts are based on the amount of steam used as shown by either 
steam or condensation meters. This contract is used: 

1. By central steam companies who furnish a house-to-house service 
and deliver the steam from a central plant to the curb wall of the customer. 

2. By maintenance companies which operate the boiler plants in 
various buildings and supply steam to the owner from his own plant on 
a meter basis. 

The result of an examination of the meter rates for steam heat for 
39 cities is shown by the following table. 

Meter Rates for Steam Heat 





Pounds of steam 
per month 


Cents, per 1,000 lb. 




Maximum. 


Minimum 


Average 


1st 

2d 

3d 


10,000 
10,000 
10,000 
10,000 
10,000 
25,000 
25,000 
50,000 
50,000 
300,000 
500,000 


100 
90 
90 

87 
85 
80 
80 
73 
70 
67 
50 


60 
50 
50 
45 
45 
43 
40 
38 
38 
36 
35 


80.0 
70.0 
67.5 


4th 

5th 


65.0 
62.5 


Next 

Next 

Next :.. . 

Next 


60.0 
57.5 
52.5 
50.0 


Next 

Over 


47.5 
41.5 







DISTRICT HEATING 337 

In a hot-water heating franchise the meter rate is not necessary, 
because there are no meters on the market. When they do come, they 
will probably be the heat-unit meter, and in that event 1,000,000 B.t.u. 
would be the logical basis of charge. 

On a meter basis for steam heating, 1,000 lb. of steam is the basis of 
charge 

On a flat-rate basis for hot water or steam heating the charge per 
annum or per season is either per square foot of radiation or per 1,000 
cu. ft. of space heated. 

When the charge per square foot of radiation is used as a basis it 
should be stated clearly that it is the radiation required to heat the build- 
ing and not the radiation that is installed in the building. The required 
radiation is the amount necessary to install so that the company can 
guarantee to maintain a comfortable temperature. 

With the flat rate per square foot basis, thermostatic control is almost 
essential to good operation and economical use of heat in the residences 
and buildings. 

The flat-rate basis charge, of so much per thousand cubic feet of space, 
is not as equitable as the per square foot of radiation basis. For each 
and every 1,000 cu. ft. of contents do not require the same amount of 
heat, owing to the difference in location and difference in use. For in- 
stance, 1,000 cu. ft. in a corner drug store requires more heat at zero out- 
side than does 1,000 cu. ft. in a dentist's office at zero outside. This 
method is not used very much at the present time. The most scientific 
method of charge and one that is finding universal favor in connection 
with public utility service is the '^ ready to serve" or ''maximum demand" 
rate. 

For example, assume a building that uses heat only 6 hr. out of 24 hr. 
in a day. This building demands a place on the line and requires the 
capacity, both in the mains and at the heating station, to supply its 
maximum demand. The heating company must be ready to serve this 
building at any time it requires service. In return for that required con- 
dition, the heating company only receives pay for 6 hr. service, while the 
building using heat for 18 hr. pays the company three times the revenue 
paid by the other building. 

It is also the case with churches or auditoriums where heat is used only 
two or three days out of the week. The heating company must reserve 
capacities for these buildings, but in return receives only about one-sixth 
the revenue it would receive from other buildings requiring the capacities 
that these churches, etc., require. It is obvious, therefore, that a rate 
based on the number of pounds of steam condensed is far from equitable. 

It is here that the "maximum demand" or "ready to serve" rate 
shows its strong points as an equitable rate. As stated before, this 



338 ENGINEERING OF POWER PLANTS 

rate is based on the cost of the service to the utility, plus an equitable 
profit. 

In making a rate for service per season it is desirable to know the per- 
centage of heat used in any one month during the heating season for two 
reasons: First, the collections are often made monthly; second, it some- 
times happens that a credit or debit is given for certain months during 
the season, when the service is started or stopped in mid-season. The 
following table will be useful in this connection. 

Heat Consumption Table 

Per cent. 

Heat used up to Oct. 31 6 

From Oct. 31 to Nov. 30 12 

From Nov. 30 to Dec. 31 18 

From Dec. 31 to Jan. 31 21 

From Jan. 31 to Feb. 28 19 

From Feb. 28 to Mar. 31 13 

From Mar. 31 to Apr. 30 8 

From Apr. 30 to May 15 3 

100 

The following division is used extensively in flat rate contracts and is 
easily remembered by the consumers: 

5 per cent, of contract price payable Oct. 1. 
15 per cent, of contract price payable Nov. 1. 
20 per cent, of contract price payable Dec. 1. 
20 per cent, of contract price payable Jan. 1. 
20 per cent, of contract price payable Feb. 1. 
15 per cent, of contract price payable Mar. 1. 

5 per cent, of contract price payable Apr. 1. 

Before leaving the subject of rates, it might be well to call attention 
to the two-rate system, which has been frequently advocated, viz., the 
adoption of a primary charge based on the theoretical amount of radia- 
tion connected and a secondary charge based on the meter readings. 
This kind of rate is perhaps more thoroughly sound than the single sliding- 
schedule, due to the fact that the primary rate can be made to closely 
approximate the investment charge, while the secondary rate can be used 
on the operating costs. The chief objection to this rate is that it requires 
that the theoretical radiation for each customer be figured from a basic 
formula and such estimates of theoretical radiation required are more 
open to controversy than the reading of a satisfactory meter. Another 
point in favor of the simple sliding-schedule based on meter readings is 
that it is more easy to explain this method of charging to the customer. 

While it is very possible that the two-rate system will be the future 



DISTRICT HEATING 339 

basis for the sale of steam, just as it is already to a large extent the basis 
for the sale of electricity, yet it is questionable as to whether the time 
for this change has arrived. 

One two-rate system in use in an eastern city is applied as follows: 

(a) Reduce the cubic feet of heated contents to a cube of equal con- 
tents. 

(6) Base the rate on the area of one side of this cube and on the actual 
steam consumption. 

For the city in question the rate is 1 ct. per square foot of the equiva« 
lent cube plus 30 cts. per 1,000 lb. of steam. 

Take a house of approximately 20,000 cu. ft. of heated contents. 
Equivalent cube = 27 X 27 X 27. Fixed charge each month of heating 
season (8 months) = 27 X 27 X SO.Ol = S7.29. 

If the steam consumption for a month were 20,000 lb., the bill for the 
month would be 

Fixed charge = $7 . 29 
20 X 30 cts. = 6 . 00 



$13.29 

If the consumption for the month were 50,000 lb. then the bill would 
be 

Fixed charge = $7.29 
50 X 30 cts. = 15.00 ■ 



$22.29 



Cost of Exhaust Steam Heating. — The Wisconsin Railroad Commis- 
sion, in its reports, vol. 2, page 302, states that, with coal at $2 per ton, 
exhaust steam could be sold at 50 cts. per 1,000 lb. safely; that is, with 
a secure profit, but it also states that where live steam is sold there would 
be small profits unless large quantities of steam were sold. 

The engineer of a company of recognized standing states that the 
charge which his company makes to the different buildings and depart- 
ments for the use of exhaust steam for heating is at the rate of 2 cts. per 
month per square foot of radiating surface for 6 months of the year. 

He finds in practice that when using exhaust steam 1 lb. will supply 
about 3 sq. ft. of radiation with steam for 1 hr. He figures that if 1 lb. 
of coal will produce 8 lb. of steam, it will supply about 25 sq. ft. of radia- 
tion for 1 hr., and when coal costs $2 per ton the fuel necessary to supply 
1 sq. ft. of radiation for one month, making proper allowance for the value 
of the steam used in the engine, will cost about 1 ct., assuming that steam 
is supplied to the radiator for only 10 or 12 hr. per day. 

Also assuming that the amount of boiler-room expense will just about 
equal the fuel cost, he estimates the cost for exhaust steam as 2 cts. per 



340 



ENGINEERING OF POWER PLANTS 



square foot per month during the months when heat is necessary. It is 
very doubtful whether many heating plants can be operated for heating 
alone and supply live steam at a cost of 2 cts. or less per square foot per 
month. 

The normal consumption of steam in radiators per season under 
ordinary conditions in a climate similar to that of Chicago, 111., runs from 
600 to 800 lb. of steam per square foot where the radiating surface is 
properly proportioned. There are buildings, however, which cannot be 
depended upon to run very close to this average. Occasionally the con- 
sumption will be very much above this amount in one building and in 
another building it will be very much below, the amount used running 
all the way from 300 to 3,000 lb. per square foot of radiating surface during 
the heating season. 

The following summaries present interesting data showing the varia- 
tions in steam consumption in different latitudes. 

Class of buildings — office buildings, retail stores, residences, saloons, 
hotels, apartments, garages, light manufacturing buildings, wholesale 
stores, clubs, schools, churches, offices, banks, lodges, factories, theatres, 
restaurants, post offices, Y. M. C. A.'s, halls, telephone companies, hos- 
pitals, city halls, court houses, etc. 

Large City in the Middle West 
Mean Temperature during Heating Season 41 °F. 



Number of 
consumers 


Cubic feet of 
space 


Square feet 
of radiation 


Total condensa- 
tion per season, 
pounds 


Season's average 

per 1,000 cu. ft. of 

space, pounds 


Season's average 
per sq. ft. radia- 
tion, pounds 


162 


20,505,000 


229,842 


117,196,000 


5,715 


510 


Eastern City 
Mean Temperature during Heating Season 41.3°F. 


187 


7,258,293 


94,993 


63,249,000 


8,714 


665 


Large Southern City 
Mean Temperature during Heating Season 54.7°F. 


149 


24,546,000 


194,702 


84,711,000 


3,451 


435 


Steam Co 


nsumption of Various Classes of Buildings in a City 
West, Indicating the Economy Effected by Meter 
' Meter rate 


of the Middle 
Rates 


39 


7,103,028 


65,132 


38,012,000 


5,352 


584 




rial rate 




95 


7,859,357 


78,062 


74,318,000 


9,456 


951 



DISTRICT HEATING 341 

Estimating Miscellaneous Steam Requirements in Large Buildings. — 

In addition to heating service the district-heating company may be called 
upon to supply steam for many other purposes The owner of the 
modern first-class building is obliged to provide the highest quality of 
service for his tenants, and this is accomplished only by the installation 
of a system of auxiliary apparatus of various kinds, many of which are 
operated by steam. Among these may be included the following: 

1. Hot-water heaters, supplying heated water for industrial or manufacturing 
purposes, or for domestic uses, such as scrubbing and lavatories. 

2. Vacuum pumps, used in connection with steam-heating systems for removing 
air and condensation from the radiation. 

3. Ejectors used in a manner similar to vacuum pumps. 

• 4. House pumps used for elevating the domestic water supply to the roof of the 
building where it is stored in a tank. 

5. Boiler-feed pumps. 

6. Steam-hydraulic elevator pumps. 

7. Direct-steam elevator engines. 

8. Fire-pumps. 

9. Air compressors. 

(a) General use. 

(6) Sewer-ejector system. 

(c) For pressure-tanks on hydraulic system. 

10. Steam syphons and jets. 

11. Refrigerating machinery. 

(a) Compression systems. 
(6) Absorption systems. 

12. Brine pumps or other auxiliary refrigerating apparatus. 

13. Drinking-water pumps. 

14. Stoker engines. 

15. Ventilating fan-engines. 

16. Warming and cooking apparatus for restaurants. 

17. Laundry apparatus. 

18. Miscellaneous industrial uses, varying with the class of building and tenants. 

To determine with any degree of certainty just how extensive the 
use of steam for these purposes will be in each building, usually requires a 
specialist in this particular line of engineering — one who is enabled to 
draw from experience and observation for verification of estimates. 
Whenever possible, it is needless to say one should be guided by com- 
parison with buildings already supplied with approximately similar 
service. 

The cost of heating service is made up of the following items which 
should be figured on the basis of 1,000 lb. of steam generated or a mul- 
tiple of that quantity. 



342 



ENGINEERING OF POWER PLANTS 



1. Fixed charges based on investment in: 




Building, 


Dynamos, 


Boilers, 


Furnaces, 


Piping, 


Engines. 


and various accessories for the above. 




(a) Amortization. 




(6) Obsolescence. 




(c) Interest. 




(d) Taxes. 




(e) Rental value of space. 




(/) Marginal charge for diversion of capital. 





Salaries < 



Operating costs : 

.Chief engineer. 

Assistant engineers. 

Firemen. 

Coal-passers. 

Oilers. 

Electricians. 

Steam-fitters. 

Boiler-washers. 

Elevator repair men. 

Helpers. 

Engineer's clerk. 

Office labor for metering and billing. 

Employer's liability insurance and salaries paid to injured employees 

when off duty. 

Also a portion of the time of the management used in buying supplies and looking after 
the operating organization. 
' Fuel. 

Transportation of ashes. 

Oil, waste, water. 

Shovels, fire-tools. 

Electricity for lighting and power in boUer room. 

Miscellaneous supplies and expenses. 



Supplies 



All of the above are direct costs which are directly chargeable to the 
cost of operating a plant. In addition to the above costs, there are 
other costs which might be termed indirect charges which often come 
as a result of power-plant operation. 

1. Throwover Switch Service from Central-station Service. — As a rule, 
the cost per kilowatt-hour for throwover switch service is greater than 
the rate where complete service is furnished, and often a minimum bill 
is required in addition to the higher rate. 

2. Danger of Breakdown in the Service and Consequent Loss if Throwover 
Switch is not Installed. 

3. Losses on Account of Decreased Rental Value of the Building. — The 
majority of isolated plants operated with high-speed engines shows a 
marked fluctuating quality in the light. This is usually increased at 
irregular intervals where high-speed electric elevators are operating on 



DISTRICT HEATING 343 

the same plant, it is also frequently found that in the summertime the 
space directly above the boiler is hard to rent on account of the heat 
coming up through the floor from the engine room below. There is also 
the damage and annoyance caused by vibration in the building. 

4. Losses of Time on Account of Obstruction of Entrances by Coal 
Teams,— Some of the firms which have discontinued the use of their 
own plants and gone on central-station service have been particularly 
desirous of getting the steam service also in order that they might 
discontinue the delivery of coal to their buildings, and thereby be able 
to receive and deliver goods without any interference with coal teams. 

5. Losses on Account of Smoke Fines, or Dirt in the Building, due to 
Operation of the Boilers. — In large Western cities where soft coal is used, 
there has been an active campaign started to prevent the emission of 
smoke, and a number of these cities have laws imposing fines on the 
owners of smoky chimneys. 

6. Losses on Account of Strikes, due to Labor Troubles. — If the above 
costs of operation are carefully tabulated and are based not on the theo- 
retical economy of apparatus operating at maximum load when new and 
under special conditions, but on the average operating economy as found 
in plants, they will show a substantial saving by the use of central- 
station service, providing the rates for central-station service correspond 
with those recently made in many of our large cities. 

The percentage distribution of cost of operation of a non-byproduct 
steam heating plant, serving approximately 500 dwellings, churches, 
etc., was as follows in 1919: 

A. Station charges : Per cent. 

Coal, $5.66 per ton 64 

Labor 21 

Oil, waste, water and supplies 3 

Maintenance, steam plant 6 

Maintenance, mains, meters, etc 6 

100 

B. General charges: 

Salaries, postage, etc., carfares, office supplies, telephones, legal expenses, 
bad debts, etc., were equivalent to about 65 per cent, of the cost of 
labor, oil, waste, water and supplies. 

C. Fixed charges: 

Depreciation, insurance and taxes 5 per cent, on investment. 

Allowable return 7 per cent, on investment. 

12 per cent. 

Heating Station. — Gifford states that in the heating station we have 
the same general subdivision in our subject, (1) steam and (2) water. 



344 ENGINEERING OF POWER PLANTS 

Steam systems divided into (a) vacuum and (6) pressure, and water 
systems are divided into (a) open and (6) closed systems. 

Steam System. — The vacuum system has a low pressure on the steam 
main and a vacuum or suction on the return main. Pumps are used to 
create the vacuum and thereby to cause the return water to come back 
to the plant. 

Its operation is as follows: The steam is generated in the boiler 
and passes either through the engines, after which the oil is extracted, 
or direct to the pipe line. Through the pipe line it goes to the buildings. 
It is there condensed and the condensation returns to the plant via the 
return line and is usually emptied into a storage tank. Here it is stored 
until the boilers need it. It passes from the tank to the feed-water 
heater, then through the economizer, if one is used, and then into the 
boiler again. 

The pressure system is like the above except that there is no return 
and, consequently, no vacuum pump. The pressure carried on this system 
is optional with the designer, but better practice seems to be to keep the 
pressure as low as possible, especially if the engines exhaust into the heat- 
ing mains. Some engineers design, in straight-fuel-burning plants, 
high-pressure systems and reduce the pressure at the service of each 
building or in the high-pressure feeder lines, but this practice has never 
been very popular and its advantages have never been proven. The mod- 
ern practice seems to be a low-pressure system (3 to 10 lb.) with high- 
pressure feeders to be used as such only when necessary. 

The operation of a pressure system is very simple. The steam is gen- 
erated in the boilers and goes from there to the engines and then to the 
pipe line, if an exhaust steam plant. If not, the steam goes direct to 
the pipe line and through the pipe line to the buildings. Here it is 
condensed and the condensed water cooled as much as possible and then 
dumped into the sewer. 

The pressure system is used more extensively than the vacuum system. 

The vacuum system allows a somewhat lower pressure on the engines 
and also furnishes the return water for reuse, which is a benefit sometimes. 

Water Systems. — The open system of hot- water heating gets its name 
from the fact that the system is open to the atmosphere at one point. 
In this system we find the open heater or com-mingler used. The 
operation is as follows : The water returns from the pipe line and passes 
through a relief valve to the open heater or com-mingler where it is 
reheated to as high a degree as there is exhaust or live steam to heat it. 
It then goes through the circulating pump and is forced, if sufficiently 
heated, out into the line again. If not sufficiently hot it is forced through 
a closed high-pressure condenser or heater, or through a circulating 
boiler where it is reheated more, before going out into the pipe line and 



DISTRICT HEATING 345 

to the buildings. After it goes through the buildings it returns to the 
plant again. 

In this system the steam and circulating water mix in the open heater 
or the com-mingler and water is, therefore, added to the system. Con- 
sequently, it is necessary to supply some means of relief which is done by 
placing a relief valve on the return line; when the pressure exceeds a 
certain point, which it will do if water is added, the valve will open and 
discharge into the storage tank. This can also be accomplished by float- 
ing the storage tank on the return line and letting the overflow go direct 
to the tank, but this arrangement does not allow any appreciable change 
in the return pressure, which change is sometimes desirable. 

The advantage of this system is that all the heat in the steam is 
transferred into the circulating water, this giving us a high efficiency 
in the transmission of the heat, but it requires more energy in the pump- 
ing of the water due to the reduction in the pressure which is necessary 
in order to mix the steam and water and liberate the air. 

Liberating or extracting the air is simple in an open heater because the 
pressure -on the heater is the same as the atmosphere and a vent open 
to the air will carry off the air. In a com-mingler where from 3 in. to 16 
in. of vacuum is maintained on the exhaust steam line it is not so simple, 
but this can be accomplished by means of tanks which work very well. 

The difference in operation between a com-mingler and an open heater 
is that the com-mingler will create a vacuum on the engine exhaust and 
the open heater will not. However, the com-mingler will operate at 
atmospheric pressure if it is desired. 

The open system throws all the condensed steam into the heating 
mains, which is an advantage in one way, in that it keeps the heating 
mains full of good water and is a disadvantage in that it takes this water 
away from the boiler. But with a tight pipe line the water discharged 
from the overflow of the pipe line soon becomes fairly good because all 
make-up water is condensation and, consequently^ the water for the boil- 
ers, which should be taken from the storage tank, will soon be diluted 
with sufficient good water to make the feed water fairly good, so that 
this disadvantage is not troublesome. 

The closed system of hot- water heating operates as follows: The 
water returns to the plant and goes through the circulating pumps. In 
this way the pumps handle the coolest water, which is some advantage. 
Then it goes through the exhaust steam condenser or heater and then, if 
not sufficiently warm, it goes through the high-pressure steam heater or 
the circulating or reheater boilers. Sometimes the circulating water is 
forced through economizers. This is a very good arrangement. After 
the water is reheated sufficiently, it is forced out through the pipe line 
through the buildings and back to the plant. 



346 ENGINEERING OF POWER PLANTS 

The closed system operates on less power requirements in its circula- 
tion of water. The fact that it does not mix the steam with the water 
insures good feed water for the boilers. The heat transmission of the 
condensers or closed heaters in this system is not as great as in the open 
heater or com-mingler in the open system. All water entering the sys- 
tem should be treated so as to take out as many of the impurities as pos- 
sible and thus keep the line in good shape by putting in only good water. 

Which system to adopt is a question that can be decided only after 
local conditions are known. It is a difficult matter sometimes to deter- 
mine — and generalities in this connection are misleading. If a steam 
plant is decided upon, it is not difficult to figure out which system, vacuum 
or pressure, will be the most economical. If a water plant has been 
chosen, it is more difficult to decide whether an open or a closed system 
will be the better. If a vacuum is desired on the engines, an open system 
with a com-mingler is a desirable and logical choice. If there are no 
engines to be considered as, for instance, in a straight-fuel-burning plant, 
a closed system answers the purpose better than an open system because 
it requires less power to handle the circulation. A closed system will 
create a vacuum if the condenser surface is sufficiently large and the water 
temperature is not carried too high and if there is not too much steam to 
condense. As a general rule, if the hot- water plant is a byproduct to an 
electric plant, an open system is the better. If not a byproduct plant, 
the closed system is, perhaps, preferable. 

After the system has been decided upon, the details of the design can 
be determined. In deciding upon these points capacity and efficiency 
are the main features to be considered. Durability is also important and 
so is the expense of maintenance. 



CHAPTER XVIII 



THE POWER PLANT OF THE TALL OFFICE BUILDING^ 

Probably the best illustration of compact power installations to meet 
the heating, ventilating, lighting, power and sanitary demands of a good- 
sized town or small city is found in the plants of tall office buildings and 
modern hotels. 

Data from 17 such plants show the cost of electric current to be made 
up of labor, coal and handling ashes, water, lamps, oil and supplies, re- 
pairs, central station service where used for periods of minimum consump- 
tion to allow shutting down of the plant, and interest and depreciation. 

Roughly these figures average: labor, J^; coal, J^; interest and depre- 
ciation, }{o or more; and the sum giving the cost of power as made up 
of the minor items. 

The mean load throughout the day is usually about 50 per cent, of the 
full load. The maximum load is required only an hour or two in the after- 
noon during the winter months. It is customary to allow about 50 per 
cent, reserve over the estimated peak loads in designing the boiler plant. 

Division of the Load. — The average power required during the differ- 
ent portions of the year is shown in the following table : 



.- 


Per cent, 
of total 


Lights, 
kw. 


Power, 
kw. 


Total, 
kw. 


Absolute peak load 


70 
60 

30 
30 
20 
16 


214 
184 
92 
92 
62 
49 


20 

20 
20 
20 
20 
20 


234 


Average peak and running load, dark days 

Average peak load for 8 months 


203 
112 


Average day load for 8 months 


112 


Average day load for 6 months 


82 


Average low days for 12 months 


69 


Average nights, Sundays and holidays 


50 







In addition to the above there is usually an increase of 10 per cent. 
over the above running loads on account of the special needs of tenants. 

Under ordinary conditions it is customary to allow 1.6 hp. in engines 
for each kilowatt output of the generator and 1.8 hp. in boilers for each 
kilowatt in generators. 

Selection of Plant. — In accordance with the above the following main 
plant would be selected, which gives elasticity in its working and will 
take care of the following conditions: 

1 Summarized from "The Power Plant of the Tall Office Building" by J. H. 
Wells, Transactions A.S.M.E., vol. 25, p. 685. 

347 



348 ENGINEERING OF POWER PLANTS 

1. Maximum load 70 per cent, of total connected load + 10 per cent. 
= 257 kw. 

2. Average day load for 8 months 30 per cent, of total connected 
load -f- 10 per cent. = 123 kw. 

To operate under these conditions the following plant will meet the 
requirements. 

Two generators of 125-kw. capacity each, either of which will carry 
the average peak running load, or both connected will carry the absolute 
peak loads which are on for short isolated periods only. 

One generator of 100-kw. capacity to carry early running and low 
average loads for 12 months. 

One generator of 50-kw. capacity as an auxiliary unit for nights, 
holidays, Sundays and odd times. 

Such a -plant in operation was called upon for the following: 

Kilowatt-hours of lighting load 

January 33,670 May 19,301 September 17,688 

February 25,388 June 18,200 October. 25,542 

March 24,462 July 16,600 November 33,696 

April 19,950 August 17,928 December 40,425 

Assuming, therefore, a total output through the busbars of 431,050 
kw.-hr. per year, the engines would generate 

1.6 X 431,050 = 689,680 hp.-hr. 

and the boilers would generate 

1.8 X 431,060 = 775,890 hp.-hr. 

Assuming an engine guarantee of 24 lb. of steam per hp.-hr. and 8 lb. 
of water per pound of coal, then the total coal will be 1,164 tons and the 
water required will be 297,942 cu. ft. 

It is safe to assume that only 50 per cent, of the water is wasted and 
the remainder returned to the boilers. 

Taking cost of coal at $3.75 per ton; water at 10 cts. per 100 cu. ft. 
(New York prices); oil and waste at $4.60; interest and depreciation 
(if one-half be charged to this account), $3,000; ash removal, $218.25 
(5 per cent, of cost of coal); and charging one-half the cost of the force 
in the fire and engine rooms to this account, or $2,500, makes the total 
cost of operating the electric plant $10,632, or approximately 2.5 cts. 
per kw.-hr. 

Estimating Boiler Capacity Required. — Hubbard gives the following 

methods of computing the boiler capacity required in office buildings. 

. Heating. — Boiler power for heating is usually obtained from the 

amount of radiating surface to be supplied, and for all practical purposes 

the following ratios may be used, in v/hich it is assumed that 1 boiler 



POWER PLANT OF THE TALL OFFICE BUILDING 349 

hp. will supply 130 sq. ft. of direct cast-iron radiation, 100 sq. ft. of 
direct wrought-iron pipe coils, 50 sq. ft. of indirect cast-iron radiation. 
Boiler power computed in this manner should be increased about 5 per 
cent, for losses due to radiation from steam and return mains. 

Ventilation. — Boiler power required for ventilation is based on the 
volume of air to be supplied. This may be found by the rule that the 
horsepower is equal to the cubic feet of air to be warmed per hour from 
zero to 70°, multiplied by 1.3 and divided by 33,000. 

Power for Lights. — In finding the boiler power for lighting, first 
determine the electrical energy to be supplied at the lamps, then find 
the indicated horsepower of the engines necessary to produce this, and 
then compute the probable quantity of steam required from the type 
of engine to be used. 

In computing the approximate electrical horsepower at the lamps it 
may be assumed that in general for offices, assembly halls, etc., approxi- 
mately 1.25 watts will be required per square foot of working plane for 
good lighting. 

The efficiency of a first-class generating set, including the losses in 
transmission, may be taken as about 75 per cent, when located in or near 
the building to be lighted, so that the electrical horsepower necessary to 
supply the lamps divided by 0.75 will give the indicated horsepower of 
the engines. 

The total weight of steam required, in pounds per hour, divided by 
30, will give the approximate boiler horsepower. 

Driving Fans. — Power for driving the fan motors may be included 
with the power for lighting, by assuming 1 hp. of electrical energy deliv- 
ered to the motors for each 2,000 cu. ft. of air to be removed by the fans 
per minute. 

Hot Water. — The boiler power for hot-water heating may be deter- 
mined by multiplying the number of gallons of water to be heated per 
hour by the increase in temperature and by 8.3, then divide by 33,000 to 
reduce to horsepower. The temperature increase may be taken as 
140° under average conditions. 

Elevators. — The horsepower required for raising an elevator is found 
by multiplying the sum of the live load, which averages about 70 lb. 
per square foot of floor space in the car, and the unbalanced weight of 
car, which may be taken as approximately 25 lb. per square foot of floor 
space in hydraulic elevators, and for drum and duplex electric elevators, 
by the speed in feet per minute, average 400 to 600. Divide this product 
by the efficiency, average about 0.6, and divide again by 33,000 to reduce 
to horsepower. 

Allowing for stops and time when the elevators are idle it is customary 
to consider that each elevator is in operation 0.7 of the time. As hydrau- 



350 ENGINEERING OF POWER PLANTS 

lie elevators are not counterweighted up to their full weight, they descend 
by gravity, so power is required only on the upward trip. 

The above rule is for a continuous upward movement, hence, if the 
elevator is in operation only 0.7 of the time, and one-half the time that 
it is in actual operation is occupied in downward trips, requiring no 
power, the results found by the above calculation should be multiplied 
by 0.7 times 0.5 when considering a hydraulic elevator. Substituting 
the average values as given above shows the required horsepower for 
each square foot of floor space in the car to be 

(70 + 25) X 400 X 0.7 X 0.5 -^ 0.6 X 33,000 = 0.7 

Hence, the total square foot floor area of the elevator cars multiplied by 
0.7 will give the horsepower to be delivered by the pumps. 

The necessary boiler power will depend upon the type of pump used. 
The following table gives the average steam consumption in pounds per 
delivered horsepower per hour for different types of duplex pumps. 

Rate of steam 
Type of pump To3p°e?' 

horsepower-hour 

Simple non-condensing 150 

Compound non-condensing 85 

Triple non-condensing 45 

High-duty non-condensing 35 

The total horsepower required multiplied by the rate of steam con- 
sumption divided by 30 will give the boiler horsepower. 

For electric elevators the foot-pounds per minute are readily deter- 
mined and hence the horsepower for each square foot of floor surface in 
the cars. 

Assuming a combined efficiency of 0.65 for the engine, generator and 
motor, the indicated horsepower of engine square feet of floor surface in 
the cars is determined and this multiplied by the total floor space, in 
square feet, will give the total indicated horsepower of the engines. From 
this point on the method of obtaining the boiler horsepower is the same 
as already described in the case of electric lighting. 

Refrigeration. — The capacity of a refrigerating plant is commonly ex- 
pressed in two ways: ''ice-melting effect '^ and ''ice making.'^ For ex- 
ample, a 20-ton machine will produce the same cooling effect in 24 hr. 
as the melting of 20 tons of ice, or in other words, will extract the same 
amount of heat from the brine as would be required to melt 20 tons of ice 
into water at a temperature of 32°. 

Theoretically, the extraction of this amount of heat from 20 tons of 
water, at an initial temperature of 32° should change into ice; but in 
practice there are various losses not present in the simple process of cool- 
ing, so that it is customary to allow for twice the boiler power per ton 



POWER PLANT OF THE TALL OFFICE BUILDING 351 

for ice making as for the process of cooling or ice-melting effect. The 
indicated horsepower required per ton of refrigeration depends upon 
the suction and condenser pressure, which in turn are governed by the 
temperature and amount of the condensing water used. 

Under conditions where condensing water must be obtained at average 
city prices the most economical results are obtained with suction pressures 
ranging from 20 to 30 lb. and condenser pressures of 140 to 150 lb. Under 
these conditions one i.hp. in the steam cylinder will produce about 60 lb. 
of ice-melting effect per hour, or 0.75 ton per 24 hr. This will, of course, 
vary somewhat with the range of pressures and also with the size and 
type of machine, but in the absence of more exact data, may be used for 
approximate results. Another method in common use is to provide 1.5 
i.hp. per ton of refrigeration, which is slightly more than the previous 
case. Knowing the indicated horsepower of the compressor, the probable 
steam consumption can be determined for the particular type of engine 
used. 

Comparative Costs of Private and Central Station Heating and Power. 
■ — To illustrate the comparative costs of private plants vs. central station 
heating and power, Bushnell and Orr present^ the following figures from 
a building recently analyzed in Chicago. This building is a large office 
building about 200 ft. square and 21 stories in height. 

It has a court in the center above the first floor 73 ft. square. The 
original estimate of the steam consumption based on formulae was 
63,200,000 lb. The actual consumption during the year 1913 as shown 
by meters was in round numbers 64,300,000 or about 1,100,000 lb. over 
the estimate. 

As the steam consumption in any building will vary ordinarily a much 
larger percentage from season to season, the estimate given may be con- 
sidered fairly accurate. The original estimate for consumption of elec- 
tricity was 1,250,000 kw.-hr. The consumption in 1913 was 1,100,000 
kw.-hr. If a plant had been installed in the building, the consumption 
would probably have been about 50,000 kw.-hr. more, and as the building 
is not quite rented a complete rental of the building would probably bring 
the current consumption very nearly up to the estimate. 

The actual consumption for this building was in round numbers 
500,000 kw.-hr. for tenants' lighting, 150,000 kw.-hr. for public lighting 
and 450,000 kw.-hr. for power, of which about three-quarters was con- 
sumed by the elevator equipment. Assuming a price for electricity of 
23-^ cts. per kw.~hr. from the central-station service and a price of 
40 cts. per 1,000 lb. for steam on central-station service, it is very easy 
to figure the cost of central-station service on this basis. Let us assume 
that the building will be fully rented and that the total consumption is 

1 Bushnell and Orr, "District Heating." 



352 ENGINEERING OF POWER PLANTS 

1,150,000 kw.-hr. We will also assume that the building purchases its 
entire requirements both for steam and electricity and retails the elec- 
tricity to its own tenants. The total bills for the building would be: 

1,150,000 kw.-hr. at 2}i cts. per kilowatt-hour $28,750 

64,300,000 lb. of steam at 40 cts. per 1,000 lb 25,720 

Total ■ $54,470 

In figuring the cost of isolated plant service, it will be necessary 
to add the cost of electricity for lights in engine and boiler rooms, and 
also the cost for ventilating same. Assuming, therefore, that this amounts 
to 50,000 kw.-hr. per year, the total electricity used by the plant w^ould 
be 1,150,000 kw.-hr. plus 50,000 kw.-hr. or 1,200,000 kw.-hr. per year. 
The average steam consumption in office building plants as shown by a 
number of tests taken on typical installations is about 60 lb. of steam 
per kilowatt-hour throughout the year. While the above would represent 
average conditions, in this comparison it would be better to assume 50 lb. 
since in a large building such as this, it would be possible to get an 
economy above the average. 

1,200,000 kw.-hr. of electricity at 50 lb. per kilowatt-hour would 
require 60,000,000 lb. of steam per year. It is fair to assume that about 
40 per cent, of this would be saved for heating by utilizing the exhaust 
from the engines. This would leave a net steam consumption of 60 
per cent, of 60,000,000 or 36,000,000 lb. It has been shown by meter 
readings th^t the heating requirements of the buildings are 64,300,000 lb. 
of steam. Adding together the steam required for electricity and the 
steam for heating, gives a total of 100,300,000 lb. or in round numbers 
100,000,000 lb. of steam per annum. The average evaporation in this 
plant runs about 5 lb. of steam per pound of coal. If a power plant were 
operated all summer long the average evaporation would be somewhat 
higher, say 5J^ lb. of steam per pound of coal. On the basis of 100,000,000 
lb. of steam, the annual coal consumption would be 18,181,818 lb., or 
in round figures 9,000 tons. On this basis the operating expenses would 
be as follows: 

Supplies 

9,000 tons of coal at $2.75 per ton $24,750 

Ash removal, 6 per cent 1,485 

Water, for steam supply, washing out boiler and engine room, • 

etc 1,000 

Oil, waste and packing : 1,200 

Tools and miscellaneous supplies. ... 1,200 

Boiler and fire insurance 60 

Total. ? $29,695 



POWER PLANT OF THE TALL OFFICE BUILDING 353 

Labor 

Chief engineer , $3,000 

Assistant to chief engineer 1,500 

Three watch engineers 3,600 

Two oilers 1,920 

Engineer's clerk 480 

Three firemen at $840 2,520 

Two ashmen at $720 1,440 

Liability insurance and losses from sickness among 

employees 1,000 

Time of office, including manager's time for super- 
vising 1,000 16,460 

Total operating expenses $46,155 

In addition to the operating costs we must include the: 

Fixed Charges. — To take care of this building which has an aggregate 
installation of about 15,000 50-watt lamps, 200 hp. in general power 
and 600 hp. in elevator power, or a total connected equipment of about 
1,800 hp., it will be necessary to install a plant of about 1,200 kw. 
which would cost complete at $50 per kilowatt about $60,000. The 
plant would also require space of upward of 6,000 sq. ft. On the above 
basis the fixed charges would be as follows: 

Amortization at 3 per cent $1,800 

Obsolescence at 5 per cent 3,000 

Interest at 6 per cent 3,600 

Repairs at 2 per cent 1,200 

Taxes at 1 per cent 600 

Rental value of space at 50 cts. per square foot 3,000 

Marginal charge for diversion of capital at 5 per cent 3,000 

Total $16,200 

Summarizing the above gives: 

Operating charges $46,155 

Fixed charges 16,200 

Total $62,355 

It will be noted that the cost for labor to take care of the elevators, 
electric fans, etc., as well as the radiation has been omitted from both 
estimates as they are practically equal in both propositions. Comparing 
this with the above cost of central-station operation, we find a saving 
of about $8,000 per year. As^a matter of fact the central station costs 
in Chicago are slightly under these figures. If the price for electricity, 
however, were 4 cts. per kilowatt-hour and the price of steam 50 cts. per 
1,000 lb., the situation would be reversed, and there would be a saving of 



354 ENGINEERING OF POWER PLANTS 

about $16,000 in the operation of an isolated plant. In other words, the 
result is not determined by the cost of isolated plant operation, but by the 
rates offered by the central-station company. 

The above figures are given as average figures and may be found to be 
higher or lower in different localities and in different plants. The fact 
that some of the largest buildings in Chicago now operating plants are 
running at considerably higher expense than that assumed in this esti- 
mate tends to show that the estimated cost of isolated plant service is 
conservative. 

Pkoblems 

77. A 10-story office building occupies a ground area of 15,000 sq. ft. and has a 
cubic capacity of 2,000,000 cu. ft. There is 1 sq. ft. of direct cast-iron radiating sur- 
face installed per 90 cu. ft. of space. The elevator equipment is four 10-passenger 
elevators, 600 ft. per minute; one 1-ton freight elevator, 400 ft. per minute. All 
elevators are motor-driven. 

The first floor is ventilated, 10 changes of air being provided per hour. Hot-water 
service heaters will provide 1,000 gal. of water per hour at 180°F. 

The engines are simple high-speed, arranged to run condensing in summer and to 
exhaust into the heating system in winter. 

Determine the capacity of generating equipment required for the building. Will 
extra boiler capacity be required for heating ? If so, what is total capacity required. 



CHAPTER XIX 
THE POWER PLANT OF THE STEAM LOCOMOTIVE 

The most compact steam power plant in daily commercial use is found 
in the locomotive. 

Horsepower. — The indicated horsepower of the locomotive may be 
computed as for any steam engine, but it is sometimes more convenient 
to use the following formula: 

Let p = mean effective pressure in pounds per square inch. 
d = diameter of cylinder in inches. 
S = length of stroke in inches. 
M = speed in miles per hour. 
D = diameter of driving wheel in inches. 

Then for two cylinders 

pd'SM 

The indicated horsepower of some of the latest type compound loco- 
motives runs as high as 3,000. 

Efficiency. — The power required to overcome the friction of the mov- 
ing parts of the locomotive and to drive the locomotive and tender varies 
from 10 to 30 per cent, of the developed power. 

Tractive Force. — Simple Locomotives. — • 

Let F = indicated tractive force in pounds. 

p = mean effective pressure in the cylinder in pounds per 

square inch. 
S = stroke of piston in inches. 
d = diameter of cylinders in inches. 
D = diameter of driving wheels in inches. 
Then 

4:Td^pS ^ d-'pS , 

If the drop in pressure of the steam due to expansion, friction and wire 
drawing be taken into account, then the formula becomes 

O.SPd^S 



Actual tractive force = 



D 



in which P = boiler pressure in pounds per square inch. 

355 



356 ENGINEERING OF POWER PLANTS 

Compound Locomotives. — The Baldwin Locomotive Works formulae 
for compound locomotives of the Vauclain four-cylinder type are 

F = ^ + 5 

in which C = diameter of high-pressure cylinder in inches. 
c = diameter of low-pressure cylinder in inches. 
For a two-cylinder cross-compound the formula is simply 

^ C2;SX0.67P 
F = 5 

The formulae apply for speeds not over 10 miles per hour above which 
the tractive power rapidly falls off. The limit of hauling capacity of a 
locomotive is usually from one-fifth to one-fourth of the weight on the 
drivers. 

Drawbar Pull. — The drawbar pull or tractive force of a locomotive 
is the force exerted at the drawbar or connection to the train as indicated 
on a dynamometer. This force is limited by the weight on the driving 
wheels and by the power of the engine. The drawbar pull at that point 
where the driving wheels begin to slip is known as the adhesion of the 
locomotive. 

Adhesion varies with the coefficient of friction between steel and 
steel under given track conditions. The use of sand under the drivers 
is to increase the coefficient of friction. 

Values of Coefficient of Friction 

Good conditions, dry rail / = . 20 to . 25 

Maximum with sand / = . 33 

Wet sloppy rail as in fog / = 0.15 

Worst condition / = 0. 125 

Tractive force = weight on drivers X /. 

Under good conditions the drawbar pull necessary to haul 1 ton of 
2,000 lb. varies from 6 to 8 lb. on level track and increases with curves 
and grades. 

Two formulae in general use for determining the resistance are 

V 

R = 2 -\- -J {Engineering News formula). 

V 

R = S -{- -^ (Baldwin Locomotive Works formula). 

in which R = resistance in pounds per ton (2,000 lb.) on straight, level 

track, 
and V = velocity in miles per hour. 

The increased resistance due to grade is as follows: 



THE POWER PLANT OF THE STEAM LOCOMOTIVE 357 
If the grade be 1 ft. per mile, the pull required to lift 2,000 lb. will be 

!:« = »■"»»»■• 

Total resistance due to grade in pounds per ton (2,000 lb.) = 0.3788 
X rise in feet per mile. 

If the grade is expressed in per cent, the resistance in pounds per ton 
(2,000 lb.) will reduce to 20 lb. for 1 per cent, grade. 

The resistance due to curves is not easily determined. G. R. Hender- 
son in "Locomotive Operation" estimates this resistance at 0.7 lb. per 
ton (2,000 lb.) per degree of curve. 

(Degree of curve = the angle at the center subtended by a chord of 
100 ft.) 

Resistance in pounds per ton = 0.7 c. 
in which c = number degrees of curve. 

This value is greater for locomotives, often being as high as 1.4 c. 

Vh - V\ 
Resistance due to acceleration = 70 a 

in which Vi and V^ = velocities in miles per hour and S = distance in 
feet. 

Tractive Effort. — The tractive effort of modern locomotives runs 
approximately as follows: 



Passenger types 42,000- 47,000 lb. 

Ordinary freight types 50,000- 60,000 lb. 

Heavy freight types 65,000- 83,000 lb. 

Exceptional heavy freight types (Mallet compound) 90,000-160,000 lb. 



Increased Economy with Increase of Pressure. — Tests reported 
{Bulletin No. 26, University of Illinois Experiment Station) show the 
following increase in economy with increase in boiler pressure : 

Boiler pressure, lb. per sq. in 120 

Steam per i.hp.-hr., lb 29. 1 

Coal per i.hp.-hr., lb 4.0 

Effect of Speed on Average Steam Pressure. — C. H. Quereau points 
out {Engineering News, Mar. 8, 1894) that the mean steam pressure (and 
consequently the power of the engine) decreases as the speed of the loco- 
motive increases. He gives the following figures: 

Miles per hour 46 51 51 53 54 57 60 66 

R.p.m 224 248 248 258 263 277 292 321 

Pressure, lb. sq. in 51.5 44,0 47.3 43.0 41.3 42.5 37.3 36.3 



140 


160 


180 


200 


220 


240 


27.7 


26.6 


26.0 


25.5 


25.1 


24.7 


3.8 


3.6 


3.5 


3.4 


3.4 


3.3 



358 



ENGINEERING OF POWER PLANTS 



Two-cylinder compound 


Singl e-expansion 


Revolutions 


Miles per 
hour 


Water per i.hp. 
per hour 


Revolu- 
tions 


Miles per 
hour 


Water per i.hp. 
per hour 


100 to 150 
150 to 200 
200 to 250 
250 to 275 


21 to 31 
31 to 41 
41 to 51 
51 to 56 


18.33 1b. 
18.9 1b. 
19.71b. 
21.41b. 


151 
219 
253 
307 
321 


31 
45 
52 
63 
66 


21.70 
20.91 
20.52 
20.23 
20.01 



Efect of Speed on Steam Consumption. — Mr. Quereau also gives in the 
same article the foregoing table relating to the variation of steam con- 
sumption with speed. 

Depreciation of Locomotives. — Kent quotes the Baldwin Locomotive 
Works as suggesting that for the first 5 years the full second-hand value 
of the locomotive (75 per cent, of first cost) be taken; for the second 5 
years 85 per cent, of this value; for the third 5 years, 70 per cent.; after 
15 years, 50 per cent, of the second-hand value; and after 20 years, and 
as long as the engine remains in use, 25 per cent, of the first cost. 

Use of Superheated Steam. — Superheated steam is now quite gen- 
erally used in locomotive practice. Its use has resulted in increased 
steam economy and less trouble from water of condensation in the cylin- 
ders. The saving in water consumption per horsepower-hour is reported 
to be some 10 or 12 per cent, over that with saturated steam, with a cor- 
responding saving of 10 to 15 per cent, in fuel consumption. 

Recent claims for use of superheaters indicate an increased boiler 
capacity of 35 per cent, and a fuel saving of 20 to 25 per cent. At the 
present time they are even in use on switch engines. 

Mechanical Stokers for Locomotives.- — The use of mechanical stokers 
on locomotives is rapidly developing. Mr. W. S. Bartholomew^ reports 
that in September, 1915, there were about 1,000 such stokers in use in 
the United States. 

The special gains by the use of stokers is summed up by Mr. Bar- 
tholomew as follows: 

It is evident that the railroad companies and the enginemen both 
profit by the application of mechanical stokers to locomotives. 

Locomotive capacity is increased, while, strange as it may seem, the 
fireman's labor in shoveling coal and his suffering from the heat are 
materially reduced. 



1 See complete review of " Mechanical Stoking of Locomotives," by W. S. Bar- 
tholomew, Journal of the Franklin Institute, September, 1915. 



THE POWER PLANT OF THE STEAM LOCOMOTIVE 359 

The railroads secure a return on their investment from the increased 
tonnage, less expensive fuel, and other economies effected, and the men, 
individually, make more money per month with less effort. 

Small locomotives are made more powerful, and large locomotives are 
made possible. 

These and other results are being accomplished by stokers designed 
to be applied to existing power with the necessary limitations that come 
thereby, and much more may reasonably be expected in the future, now 
that the stoker has established itself for permanent use, as stokers will 
be taken seriously into account in the designing of new heavy power to 
be built in the future for capacity as well as economy. 

Powdered Fuel for Locomotives. — A great deal of attention has of 
late been given to the use of powdered fuel in locomotive practice. Some 
of the reasons for its introduction are based on the fact that for good 
boiler efficiencies the fuel rate with coal burned on grates is only from 
50 to 60 lb. per sq. ft. per hour or a total consumption of from 3,000 to 
6,000 lb. per hour for any locomotive. 

The actual requirements at times are 150 lb. per sq. ft. per hour or 
totals of from 9,000 to 15,000 lb. per hour with mechanical stokers. 
Under these conditions, the boiler efficiency drops to 55 per cent, and 
even as low as 45 per cent. 

It is claimed that with powdered fuel the normal efficiencies can be 
maintained. 

Another advantage claimed for powdered fuel is that maximum 
steam pressure can be raised in one hour from cold water. 

J. E. Muhlfeld states^ that the use of powdered fuel results in the 
elimination of smoke, cinders, sparks and fire hazard; increased draw- 
bar horsepower per hour per unit weight; reduced non-productive time 
at terminals; improved thermal effectiveness of the locomotive as a 
whole; utilization of otherwise unsuitable or waste fuels; elimination of 
arduous labor; provides greater continuity of service; and produces more 
effective and economical operation and maintenance. 



LOCOMOTIVE PERFORMANCE 

The best idea of the performance of the steam locomotive is probably 
secured by an examination of the conclusions of the special committee 
appointed to cooperate with the Pennsylvania R, R. in conducting tests 
oi locomotives at the St. Louis plant during the Exposition of 1904. The 
conclusions are as follows: 

1 Journal of the A. S. M. E., September, 1917. 



360 ENGINEERING OF POWER PLANTS 

BOILER PERFORMANCE 

1. Contrary to common assumption, the results show that when forced 
to maximum power the large boilers delivered as much steam per unit 
area of heating surface as the small ones. 

2. At maximum power, a majority of the boilers tested delivered 12 
or more lb. of steam per square foot of heating surface per hour; two de- 
livered more than 14 lb.; and one, the second in point of size, delivered 
16.3 lb. These values expressed in terms of boiler horsepower per square 
foot of heating surface are 0.34, 0.40 and 0.47 respectively. 

3. The two boilers holding first and second place with respect to weight 
of steam delivered per square foot of heating surface are those of 
passenger locomotives. 

4. The quality of the steam delivered by the boilers of locomotives 
under constant conditions of operation is high, varying somewhat 
with different locomotives and with changes in the amount of power 
developed between the limits of 98.3 per cent, and 99.1 per cent. 

5. The evaporative efficiency is generally maximum when the power 
delivered is least. Under conditions of maximum efficiency most of the 
boilers tested evaporated between 10 and 12 lb. of water per pound 
of dry coal. The efficiency falls as the rate of evaporation increases. 
When the power developed is greatest its value commonly lies between 
limits of 6 and 8 lb. of water per pound of dry coal. 

6. The smoke-box temperature for all boilers, when working at light 
power, is not far from 500°F. As the power is increased the tempera- 
ture gradually rises, the maximum value depending upon the extent to 
which the boiler is forced. For the locomotives tested it lies between 
600° and 700°F. 

7. With reference to grate area, the results prove beyond question 
that the furnace losses due to excess air are not increased by increasing 
the area. In general, it appears that the boilers for which the ratio of 
grate surface to heating surface is largest are those of greatest capacity. 

8. A brick arch in the firebox results in some increase in furnace 
temperature and improves the combustion of the gases. 

9. The loss of heat through imperfect combustion is in most cases 
small, except as represented by the discharge from the stack of solid 
particles of fuel. 

10. Relatively large firebox heating surface appears to give no ad- 
vantage either with reference to capacity or efficiency. The fact 
seems to be that the tube-heating surface is capable of absorbing such 
heat as may not be taken up by the firebox. 



THE POWER PLANT OF THE STEAM LOCOMOTIVE 361 

11. The value of the Serve tube over. the plain tube of the same 
outside diameter, either as a means for increasing capacity or efficiency, 
was not definitely determined. 

12. The draft in the front end for any given rate of combustion, 
as measured in inches of water, depends upon the proportions of the 
locomotive and the thickness and condition of the fire. Under light 
power its value may not exceed an inch, but it increases rapidly as the 
power increases. Representative maximums derived from the tests lie 
between the limits of 5 in. and 8.8 in. 

13. Insufficient openings in the ash-pans and the mechanism of the 
front end, especially the diaphragm, are shown by the tests to lead 
to the dissipation of considerable portions of the draft force. 

THE ENGINE 

14. The indicated horsepower of the modern simple freight locomotive 
tested may be as great as 1,000 or 1,100; that of a modern compound 
passenger locomotive may exceed 1,600. 

15. The maximum indicated horsepower, per square foot of grate 
surface lies, for the freight locomotives, between the limits of 31.2 and 
21.1; for passenger locomotives, between 35.0 and 28.1. 

16. The steam consumption per indicated horsepower-hour necessarily 
depends upon the conditions of speed and cut-off. For the simple freight 
locomotives tested the average minimum is 23.7. The consumption 
when developing maximum power is 23.8, and when under those conditions 
which proved to be least efficient, 29.0. 

17. The compound locomotives tested, using saturated steam, con- 
sumed from 18.6 to 27 lb. of steam per indicated horsepower-hour. Aided 
by a superheater, the minimum consumption is reduced to 16.6 lb. of 
superheated steam per indicated horsepower-hour. 

18. In general the steam consumption of simple locomotives decreases 
with increase of speed, while that of the compound locomotive increases. 
From this statement it appears that the relative advantages to be de- 
rived from the use of the compound diminish as the speed is increased. 

19. Tests under a partially opened throttle show that when the degree 
of throttling is slight the effect is not appreciable. When the degree 
of throttling is more pronounced, the performance is less satisfactory 
than when carrying the same load with a full throttle and a shorter 
cut-off. 

THE LOCOMOTIVE AS A WHOLE 

20. The percentage of the cylinder power which appears as a stress 
in the drawbar diminishes with increase of speed. At 40 r.p.m. the 



362 . ENGINEERING OF POWER PLANTS 

maximum is 94 and the minimum 77; at 280 r.p.m. the maximum is 
87 and the minimum 62. 

21. The loss of power between the drawbar and the cyHnder is 
greatly affected by the character of the lubricant. It appears from the 
tests that the substitution of grease for oil upon axles and crankpins 
increases the machine friction from 75 to 100 per cent. 

22. The coal consumption per dynamometer horsepower per hour 
for the simple freight locomotives tested is, at low speeds, not less than 
3.5 lb., nor more than 4.5 lb., the value varying with the running condi- 
tions. At the highest speeds covered by the tests the coal consumption 
for the simple locomotives increased to more than 5 lb. 

23. The coal consumption per dynamometer horsepower per hour 
for the compound freight locomotives tested is, for low speeds, between 
2 and 3.7 lb. Results at higher speeds were obtained only from a two- 
cylinder compound, the efficiency of which under all conditions is shown to 
be very high. The coal consumption per dynamometer horsepower-hour 
for locomotive at the higher speed increases from 3.2 to 3.6 lb. 

24. The coal consumption per dynamometer horsepower-hour for the 
four compound passenger locomotives tested varies from 2.2 to more 
than 5 lb., depending upon running conditions. In the case of all 
these locomotives the consumption increases rapidly as the speed is 
increased. 

25. A comparison of the performance of the compound freight 
locomotives with that of the simple freight locomotives, is very favorable 
to the compounds. For a given amount of power the compound shows 
an average saving over the best simple of over 10 per cent., while the best 
compound shows a saving over the poorest simple of not far from 40 per 
cent. It should be remembered, however, that the conditions of the 
tests, which provide for the continuous operation of the locomotives 
at constant speed and load throughout the period covered by the observa- 
tions, are all favorable to the compound. 

28. It is a fact of more than ordinary significance that a steam loco- 
motive is capable of developing a horsepower at the drawbar upon the 
consumption of but a trifle more than 2 lb. of coal per hour. This fact 
gives the locomotive high rank as a steam power plant. 

27. It is worthy of mention that the coal consumption per horsepower- 
hour developed at the drawbar by the different locomotives tested pre- 
sents marked differences. Some of these are easily explained from a 
consideration of the characteristics of the locomotives involved. Where 
the data are not sufficient to permit the assignment of a definite cause 
there can be no doubt that an extension of the study already made will 
reveal it. 



THE POWER PLANT OF THE STEAM LOCOMOTIVE 363 

Average Heat Balance for Test Locomotive. — 

Percentages op Total Heat Available 

Absorbed by the water in the boiler 52 

Absorbed by the steam in the superheater ,. . 5 

Lost in vaporizing moisture in the coal 5 

Lost through the discharge of CO 1 

Lost through the high temperature of escaping gases, the products 

of combustion 14 

Lost through unconsumed fuel in the form of front-end cinders 3 

Lost through unconsumed fuel in the form of cinders or sparks 

passed out of the stack 9 

Lost through unconsumed fuel in the ash 4 

Lost through radiation, leakage of steam and water, etc 7 

100 

Fuel Expense of Locomotives. — The fuel bills of a railroad constitute 
ordinarily about 10 per cent, of the total expense of operation, or from 
30 to 40 per cent, of the actual cost of running the locomotive. 

There were in 1906, on the railroads of the United States 51,000 
locomotives. It is estimated that these locomotives consumed during 
the year not less than 90,000,000 tons of fuel, which is more than one- 
fifth of all the coal, anthracite and bituminous, mined in the coun- 
try during the same period. The coal thus used cost the railroad 
$170,500,000. 

Observations on several representative railroads have indicated that 
not less than 20 per cent, of the total fuel supplied to locomotives per- 
forms no function in moving trains forward. It disappears in the 
incidental ways just mentioned or remains in the firebox at the end of the 
run. The fuel consumption accounted for by the heat balance is, there- 
fore, but 80 per cent, of the total consumed by the average locomotive 
in service. Applied on this basis to the total consumption of coal for the 
country, the heat balance may be converted into terms of tons of coal as 
follows : 

Summary of results obtained from fuel burned in locomotives. 

Tons 

1. Consumed in starting fires, in moving the locomotive to 
its train, in backing trains into or out of sidings, in making 
good safety-valve and leakage losses, and in keeping the 
locomotive hot while standing (estimated) 18,000,000 

2. Utilized, that is, represented by the heat transmitted 

to water to be vaporized 41,040,000 

3. Required to evaporate moisture contained by the coal.. . 3,600,000 

4. Lost through incomplete combustion of gases 720,000 

5. Lost through heat of gases discharged from the stack 10,080,000 

6. Lost through cinders and sparks 8,640,000 

7. Lost through unconsumed fuel in the ash 2,880,000 

8. Lost through radiation, leakage of steam and water, etc. 6,040,000 

90,000,000 



364 ENGINEERING OF POWER PLANTS 

Elimination of the Steam Locomotive. — During the past few years 
much has been written regarding the electrification of terminals and even 
of main lines. The development is slowly but surely coming. Although 
it is not within the field of these notes to present any lengthy discussion 
of this subject, yet the conclusions of the Chicago Association of Com- 
merce presented in its report relating to " Smoke Abatement and Elec- 
trification of Railway Terminals" (1915) are of sufficient significance to 
warrant presentation. The conclusions regarding terminal electrifica- 
tion in Chicago are: 

(a) That it is practicable from an engineering standpoint. 

(6) That when effected it will be of economic advantage to the railroads. 

(c) That it will present no greater element of danger to passengers 
and employes, if properly installed, than now exists with steam opera- 
tion. 

(d) That the most serious and difficult feature of the problem is the 
financial one. 

'' Conclusions Concerning the Feasibility of Eliminating the Steam 
Locomotive from the Railroad Terminals of Chicago and of Meeting all 
Operating Requirements without Resort to Complete Electrification." 
Basing judgment upon the present-day achievement,^ the following 
general conclusions seem to be justified: 

1. There is available at this time no form of locomotive, carrying its 
own power and capable of handling the traffic of the Chicago railroad 
terminals, which would be substituted for the steam locomotive, and there 
is no prospect of the immediate development of any such locomotive. 

2. The design of a gasoline internal-combustion locomotive capable 
of handling the traffic of the Chicago terminals would involve such a 
multiplication of engine cylinders as to make its adoption almost, if not 
quite, prohibitive. 

3. The adoption of a gasoline internal-combustion locomotive, should 
the design of such a machine become practicable, would not insure smoke- 
less operation. As in the case of an automobile engine, such machines 
emit smoke when starting, and the amount of the smoke discharged is a 
function of the power developed. 

4. The possibilities of an internal-combustion locomotive, in which the 
source of power is an oil engine, constitute a promising field for work. 
No such locomotive, possessing the power of a modern steam locomotive, 
has thus far been developed. The elaborate experiments of Dr. Rudolph 
Diesel are significant, but the results derived from them do not indicate 
ithat the problem of design has been solved. 

5. The adoption of an oil-engine locomotive of the Diesel type, as- 
suming the details of a satisfactory design to have been worked out, will 

I April, 1914. 



THE POWER PLANT OF THE STEAM LOCOMOTIVE 365 

not in itself suffice to secure smokeless operation. Oil engines are smoke- 
less only when the fuel and air supply are adjusted to suit the load. 
Whether an oil engine will be more or less objectionable, because of its 
smoke, than the existing steam locomotive, can be determined only by 
tests under service conditions. 

6. The compressed-air storage locomotive, the hot-water storage loco- 
motive and the storage-battery locomotive are all devices which, judged 
by the present state of the art, can be made serviceable only under special 
or peculiar conditions where more efficient devices cannot be used. It is 
not to be expected that such locomotives can be introduced for general 
work in the Chicago terminal. 

7. There are certain short stretches of track in yards and industries 
to which it appears impracticable to apply any form of electric contact 
system; in the event of the complete elimination of the steam locomotive 
from the Chicago terminals, it would be practicable to work this trackage 
with some one of the specialized forms of locomotive described, notwith- 
standing the fact that no one of these locomotives is sufficient for the 
general work of the terminals. 

8. The self-propelled motor cars of any of the various types described 
are most valuable for a light, diversified and not too frequent traffic. The 
field of usefulness for such cars within the limits of the Chicago terminals, 
where business is segregated and the passenger movement heavy, is not 
extensive. 

9. The complete elimination of the steam locomotive from the rail- 
road terminals of Chicago would, under present conditions, necessitate 
the abandonment of the service or the complete electrification of these 
terminals. 



CHAPTER XX 
FUELS 

Solid Fuels. — The solid fuels used for power-plant purposes may be 
divided into the following general classes: 

1. Coal. 

2. Lignite. 

3. Peat. 

4. Wood. 

According to the classification of the U. S. Geological Survey,^ the 
various groups of coal and allied compounds are: 
(a) Graphite. 
(h) Anthracite. 

(c) Semi-anthracite. 

(d) Semi-bituminous. 

(e) Bituminous. 

(/) Sub-bituminous. 

(g) Lignite. 

(h) Peat. 

(^) Wood, cellulose. 

The forms of wood in common use are : wood, bagass, tan bark, straw 
and stubble. 

Coke, charcoal and artificial fuel briquettes are fuels prepared from 
coal and wood. 

Graphite. — Graphite cannot be burned with sufficient ease to warrant 
its use as a fuel. There are, however, extensive deposits of graphitic 
anthracite in Rhode Island and Massachusetts that have been exploited 
from time to time as fuel. Its composition is approximately carbon, 78 
per cent.; volatile matter, 2.60 per cent.; silica, 15.06 per cent.; phos- 
phorus, 0.045 per cent. 

Under special treatment it has been made to burn in boiler furnaces, 
but with difficulty. Under suitable conditions it may be used for the 
generation of producer gas. 

Anthracite. — The principal anthracite mines are in eastern Pennsyl- 
vania, although semi-anthracite coal is found in one or two other sections 
of the country. Anthracite is largely carbon. The commercial sizes are 
usually known as lump, broken, egg, stove, chestnut, pea, 1 and 2 buck- 

1 Transactions A.S.M.E., May, 1905. 

366 



FUELS 367 

wheat, rice and barley. These last two are known as No. 3 in the New 
York market. The heating value of the smaller sizes is considerably 
below that of the larger sizes as the amount of non-combustible earthy 
material is naturally higher in the smaller sizes. To handle the finer 
sizes to advantage for power-plant purposes requires specially constructed 
grates and forced draft. 

Semi-bituminous Coals. — The combustible portion of semi-bituminous 
coals is very uniform in composition. The volatile matter is usually from 
18 to 22 per cent, of the combustible matter. Such fuels are usually low 
in moisture, ash and sulphur, and rank among the best steaming coals in 
the world. 

Among these coals are the Pocahontas, New River, Cumberland and 
Clearfield coals of Virginia, West Virginia and Maryland. These are 
the highest grade coals in the United States. They run low in ash, 3 to 
8 per cent, and their heating value is in the neighborhood of 14,500 B.t.u. 
per pound or better, for the higher grades. 

Bituminous Coals. — Bituminous coal is found extensively in the 
United States especially in Pennsylvania, Ohio, Kentucky, Tennessee, 
Indiana, Illinois, Iowa and Wisconsin. There is a wide variation in the 
ash content and heating value. In general the Eastern varieties are of 
a higher grade than the Western. Many bituminous coals are of the 
caking variety thus requiring considerable attention on the part of the 
firemen. 

Sub-bituminous coal, as its name implies, is a grade between bitu- 
minous coal and the true lignites. It is frequently called black lignite. 
Some of the sub-bituminous coals, however, resemble bituminous coal so 
closely in physical appearance that it is hard to distinguish between them 
except by analysis. Its calorific value is usually less than that of bitu- 
minous coal. It is usually high in sulphur. It is found in the Rocky 
Mountain and Pacific States. 

Lignite. — ^Lignite usually shows clearly a woody structure. Fre- 
quently the form of the bark of trees is plainly visible, although some lig- 
nites have more the appearance of brown clay. The lignites of the United 
States resemble the brown coals of Germany. The amount of moisture 
is very high in the lignites, often running from 30 to 40 per cent. The 
localities in which lignite is found are chiefly North Dakota, South Dakota, 
Texas, Arkansas, Louisiana, Mississippi and Alabama. 

Kent states that the relation of the volatile matter and of the fixed 
carbon in the combustible portion of the coal enables us to judge the class 
to which the coal belongs, as anthracite, semi-anthracite, semi-bituminous, 
bituminous or lignite. Coals containing less than 7.5 per cent, volatile 
matter in the combustible, would be classed as anthracite, between 7.5 
and 12.5 per cent, as semi-anthracite, between 12.5 and 25 per cent, as 



368 



ENGINEERING OF POWER PLANTS 



semi-bituminous, between 25 and 50 per cent, as bituminous and over 
50 per cent, as lignitic coals or lignites. In the classification of the U. S. 
Geological Survey the sub-bituminous coals and lignites are distinguished 
by their structure and color rather than by analysis. 

In summarizing tests of the U. S. Geological Survey (Bulletins 261, 
290 and 323 and Professional Paper 48) Kent presents the following valu- 
able table and calls attention to the fact that the table shows approxi- 
mately the range of heating values per pound of combustible, as deter- 
mined by the Mahler calorimeter, and the range of percentages of fixed 
carbon in the combustible (total of fixed carbon and volatile matter) in 
the coals from the several States. The extreme figures, 10,200 and 15,950 
fairly represent the whole range of heating values of the combustible of 
the coals of the United States, but the figures for each State do not nearly 
cover the range of values in that State, and in some cases, as in Indiana 
and Illinois, the figures are much lower than the average heating values 
of the coals of the States. 



Fixed C, 
per cent. 



B.t.u. per pound of 
combustible 



Pennsylvania anthracite . . 

West Virginia semi-bituminous 

Arkansas semi-bituminous 

Pennsylvania bituminous 

West Virginia bituminous 

Eastern Kentucky 

Western Kentucky 

Alabama 

Kansas : 

Oklahoma 

Missouri 

Illinois 

Iowa 

Indiana 

New Mexico 

Wyoming 

Montana 

Colorado 

North Dakota 

Texas , . 



89 
80.0 to 76.5 
84.0 to 77.0 

67 
67.5 to 55.0 

60 
55.0 to 50.5 
61.5 to 59.0 
62.0 to 53.5 
56.0 to 51.0 
50.5 to 47.0 
59.0 to 47.5 
57.0 to 53.5 

49 

50.5 to 47.0 

48.0 to 41.5 

48.5 

46, 
48.5 to 42.5 
44.5 to 34.0 



14,900 
15,950 to 15,650 
15,250 to 15,500 

15,500 
15,500 to 15,000 

15,000 
14,400 to 13,700 
14,800 to 14,200 
14,800 to 14,100 
14,600 to 13,100 
14,300 to 12,600 
13,700 to 12,400 
13,600 to 12,700 

13,300 
12,500 to 12,300 
13,300 to 10,900 

12,100 

11,500 
10,200 to 11,400 
10,900 to 11,000 



The following analyses of representative coals of the six classes speci- 
fied as given by Professor N. W. Lord are: 



Class 1. Anthracite culm. 
Class 2. Semi-anthracite. 
Class 3. Semi-bituminous. 



Pennsylvania. 
Arkansas. 
West Virginia. 



FUELS 



369 



Class 4 (a). Bituminous coking. Connellsville, Pa. 
Class 4 (6). Bituminous non-coking. Hocking Valley, Ohio. 
Class 5. Sub-bituminous. Wyoming, black lignite. 
Class 6. Lignite. Texas. 



Composition of Illustrative Coals, Car-load Samples. Proximate Analysis 

OP ''Air-dried" Sample 



Class 

Moisture 

Vol. comb 

Fixed carbon 

Ash 

Loss on air drying 



1 


2 


3 


4a 


46 


5 


2.08 


1.28 


0.65 


0.97 


7.55 


8.68 


7.27 


12.82 


18.80 


29.09 


34.03 


41.31 


74.32 


73.69 


75.92 


60.85 


52.57 


46.49 


16.33 


12.21 


4.63 


9.09 


5.85 


3.52 


3.40 


1.10 


1.10 


4.20 


Undet. 


11.30 



6 

9.88 

36.17 

43.65 

10.30 

23.50 



Ultimate Analysis op Coal Dried at 105°C. 



Hydrogen 
Carbon . . . 
Oxygen.. 
Nitrogen . 
Sulphur . . 
Ash...... 



2.63 


3.63 


4.54 


4.57 


5.06 


5.31 


76.86 


78.32 


86.47 


77.10 


75.82 


73.31 


2.27 


2.25 


2.68 


6.67 


10.47 


15.72 


0.82 


1.41 


1.08 


1.58 


1.50 


1.21 


0.78 


2.03 


0.57 


0.90 


0.82 


0.60 


16.64 


12.36 


4.66 


9.18 


6.33 


3.85 



4.47 

64.84 

16.52 

1.30 

1.44 

11.43 



Results Calculated to an Ash- and Moisture-pree Basis 



Vol. comb 

Fixed carbon. 



8.91 


14.82 


19.85 


32.34 


39.30 


47.05 


91.09 


85.18 


80.15 


67.66 


60.70 


52.95 



45.31 
54.69 



Ultimate Analysis 



Hydrogen 
Carbon. . . 
Oxygen.. 
Nitrogen . 
Sulphur. . 



3.16 


4.14 


4.76 


5.03 


5.41 


5.50 


92.20 


89.36 


90.70 


84.89 


80.93 


76.35 


2.72 


2.57 


2.81 


7.34 


11.18 


16.28 


0.98 


1.61 


1.13 


1.74 


1.61 


1.25 


0.94 


2.32 


0.60 


1.00 


0.87 


0.62 



5.05 

73.21 

18.65 

1.47 

1.62 



Caloripic Value in B.t.u. per Pound, by Dulong's Formula 


Air-dried coal 


12,472 
15,286 


13,406 
15,496 


15,190 
16,037 


13,951 
15,511 


12,510 
14,446 


11,620 
13,235 


10,288 


Combustible 


12,889 



Dulong's formula is 



total heat = 14,600C + 62,000(^ ~ 8^ "^ 4,000>S 



370 



ENGINEERING OF POWER PLANTS 



in which C, H, and >S represent the proportions of carbon, hydrogen, 
oxygen and sulphur. 

An approximate formula sometimes used is 

total heat = 154.8 (100 — (per cent, of ash + per cent, of moisture)). 

From a table presented by Meyer ("Steam Power Plants," page 23) 
the following data are selected to indicate the relative value of the differ- 
ent classes of steam coals: 



Kind of coal 


Relative 

evaporative 

power 


*' Equivalent 

evaporation," 

pounds 


Pounds of coal 

per square foot of 

grate per hour 


Pocahontas, W. Va.i 

Youghioheny, Pa.^ 


100.0 
91.6 
80.0 
80.0 
67.5 
84.0 
79.0 
74.0 


9.5 
8.7 
7.6 
7.6 
6.4 
8.0 
7.5 
7.0 


15 
17 


Hocking Valley, O.2 


18 


Big Muddy, 111.2 


20 


Mt. Olive, 111.2 


20 


Lackawanna, Pa.,^ pea 


15 


Lackawanna, Pa., 3 No. 1 buckwheat 
Lackawanna, Pa.,^ rice 


13 
12 







1 Semi-bituminous. 2 Bituminous. ^ Anthracite. 



Peat. — Peat is defined by Davis^ as partly decomposed and disinte- 
grated vegetable matter that has accumulated in any place where the 
ordinary decay or chemical decomposition of such material has been more 
or less suspended, although the form and a considerable part of the struc- 
ture of the plant organs are more or less destroyed. 

In its natural state peat contains about 10 per cent, combustible and 
about 90 per cent, water. 

Although peat has long been used in Europe as fuel for heating and 
other domestic purposes, it is but recently that it has been utilized for 
power purposes. Although it is estimated that in the United States, 
exclusive of Alaska, peat deposits cover an area of over 11,000 sq. miles, 
aggregating approximately 13,000,000,000 tons of available fuel, yet its 
use in this country can hardly be said to be beyond the experimental stage. 

A good idea of the heating value of peat may be had from the following 
table: 

1 "The Uses of Peat" by C. A. Davis, Bureau of Mines Bulletin No. 16. 



FUELS 
Air-dried Peat 



371 



Kind of peat 



Locality 



Water 



Ash 



Sul- 
phur 



Heating value, B.t.u. 



Calo- 



Air- 
dried 



Water- 
free 



Brown, fibrous . . . 
Brown, fibrous . . . 
Light-brown, fibrous 
Dark-brown 



Brown 

Brown, fibrous 

Brown 

Brown, fibrous 

Brown 

Brown, fibrous 

Salt marsh 

Black 

Light-brown, struc- 

* tureless 

Brown, fibrous 

Brown, sandy 

Black 



Fremont, N. H . 

Hamburg, Mich. . . . 
Rochester, N. H.. . . 
Westport, Conn. . . . 
New Durham, N. H. 
New Fairfield, Conn. 
Westport, Conn. . . . 
Kent, Conn. ....... 

Cicero, N. Y 

Black Lake, N. Y. 
La Martine, Wis, . , 

Kittery, Me 

Greenland, N. H.... 



Waupaca, Wis. 
Madison, Wis.. 

Kent, Conn 

N. Y... 



6.34 

7.50 

11.64 

12.70 

6.06 

9.63 

19.69 

12.10 

14.57 

8.68 

9.95 

13.50 

6.62 

6.62 
8.99 
9.06 
6.52 



7.93 

6.55 

4.06 

4.12 

17.92 

7.93 

3.23 

7.22 

7.42 

16.61 

16.77 

12.04 

24.11 

24.44 
18.77 
36.06 
28.50 



0.69 
0.28 
0.22 
0.24 
0.88 
0.46 
0.19 
0.83 
0.25 
0.99 
0.79 
1.94 
1.01 

0.65 
0.38 
1.46 
0.57 



5,161 
5,050 
5,042 
4,772 
4,415 
4,367 
4,273 
4,269 
4,209 
4,179 
4,149 
4,066 
3,992 

3,872 
3,857 
3,291 
2,867 



9,290 
9,090 
9,083 
8,590 
7,947 
7,861 
7,691 
7,684 
7,576 
7,522 
7,468 
7,319 
7,186 

6,970 
6,943 
5,924 
5,161 



9,920 
10,026 
10,280 
9,839 
8,460 
8,690 
9,578 
8,743 
8,869 
8,237 
8,293 
8,462 
7,695 

7,465 
7,628 
5,924 
5,521 



A typical proximate analysis of a good griade of Florida peat is: 

Moisture 17.21 

Volatile matter 51 . 01 

Fixed carbon 24.85 

Ash 6.93 

Sulphur 0.49 

B>t.u. per pound of dry fuel 10,082 

Wood. — Wood is now little used as power-plant fuel. Dry wood con- 
sists of about 50 per cent, carbon, the remaining 50 per cent, being oxygen 
and hydrogen. Some woods, such as the evergreens, contain small quan- 
tities of turpentine. 

The heat value of dry wood seems to run from about 6,600 B.t.u. per 
pound for white oak to 9,900 for long-leaf pine. Under the most favor- 
able conditions for burning ordinary wood, the heat value will not 
average over 72 per cent, of that of dry wood or in the neighborhood of 
5,700 B.t.u. The ash content varies, according to different writers, from 
0.03 to 5.0 per cent. 

When fresh cut the moisture content varies from 30 to 50 per cent., 
but after a few months of drying in the air this is reduced to 20 or 25 per 
cent. 

Approximately 2}i\h. of dry wood are required to equal 1 lb. of aver- 



372 ENGINEERING OF POWER PLANTS 

age bituminous coal. Pound for pound the fuel value of different dry 
woods is practically the same. 

When actual weights cannot be had, the following may be used: 

Lb. per cord 

Dry 3,650 

Partly seasoned 4,600 

Green 5,200 

Mixed 4,600 

There is considerable variation in the weights of different woods as 
shown below: 

Lb. per cord 
Green Air dried 

Cottonwood 4,200 2,500 

Willow 4,600 2,300 

Hickory ; 5,700 4,600 

Bagass. — Bagass is the refuse cane from the sugar manufacture. The 
composition of bagass is approximately: 

Per cent. 

Wood fiber 37 to 45 

Combustible salts 10 to 9 

Water 53 to 46 

100 - 100 

and the corresponding heat value from 3,000 to 3,500 B.t.u. per pound. 

E. W. Kerr reports^ an equivalent evaporation of 2.25 lb. of water 
per pound of wet bagass haying a net heating value of 3,256 B.t.u. per 
pound. 

He recommends a rate of burning of not less than 100 lb. per square 
foot of grate per hour. 

Other figures indicate the equivalent evaporation to vary from 2 
to 3.5 lb. per pound of bagass. 

The rate of burning is sometimes as high as 300 lb. per sq. ft. of grate 
surface. Kerr recommends a rate of not less than 100 lb. 

From 400 to nearly 600 lb. of bagass are recovered per ton of cane. 

On the basis of this evaporation it required from 4 to 6 lb. of bagass 
to equal 1 lb. of 14,000 B.t.u. coal and from 40 to 65 lb. to equal 1 gal. of 
oil of 19,000 B.t.u. per pound. 

Tan Bark. — D. M. Meyers states^ that the calorific value of spent 
tan averages : 

9,500 B.t.u. per pound, dry. 

2,665 B.t.u. per pound as fired (65 per cent, moisture). 

He reports the following economic results: 

Equivalent evaporation per pound of tan as fired, pounds 1 . 48 

Equivalent evaporation per pound of dry tan, pounds 4 . 30 

1 Bulletin 117, Louisiana Agricultural Experiment Station, Baton Rouge, La. 

2 Transactions A.S.M.E., vol. 31, p. 685. 



FUEL& 
Straw. — A summary of the data given by Kent^ is: 



373 





Per cent. 


of volume 




Dry winter-wheat 
straw 


Mean for wheat and 
barley straw 


c. . 


46.2 
5.6 
0.4 

43.7 
4.1 


36.0 


H 


5.0 


N 


0.5 


. .. ... 


38 


Ash 


4.8 


Water 


15.7 








100.0 


100.0 



B.t.u. per pound 

Winter-wheat straw, dry 6,290 

Winter-wheat straw, 6 per cent, water 5,770 

Winter-wheat straw, 10 per cent, water 5,448 

Buckwheat straw, dry 5,590 

Flax straw, dry 6,750 



Coke. — Coke is made from coal by one of two processes. Gas-works 
coke is the residue from the distillation of coal in gas making. Oven 
coke is produced by a process of partial combustion in specially designed 
ovens. For fuel purposes the latter is usually the better. With the 
beehive-oven process of coke making the percentage yield of coal in coke 
averages about 60 per cent, for the United States, the range being from 
44 to 75 per cent. With the byproduct coke-oven process the yield should 
average from 68 to 72 per cent, with good coal. The average of 29 sam- 
ples of coke from six different States shows approximately the following 
composition : 

Per cent. 

Fixed carbon 90 

Ash 9 

Sulphur 1 

Charcoal. — By driving off the volatile matter from wood or peat by a 
process of partial combustion or by a process of distillation, charcoal may 
be produced. 

The charcoal yield is from 45 to 60 bu. per cord of wood. Two cords 
of hard wood will yield about one ton of charcoal. The labor cost of 

1 "Mechanical Engineers' Pocketbook," 9th edition, 1916, p. 839. 



374 



ENGINEERING OF POWER PLANTS 



charcoal making is reported as about 60 cents per ton of charcoal. It is 
far too expensive to be used much as a power-plant fuel. 

Fuel Briquets. — By grinding coal, lignite or peat and pressing in forms 
fuel briquets may be produced. If coal is used a binder is necessary. 

Investigations by the Bureau of Mines show the following binders to 
be commercially available : 



Binder 


Amount required, 
per cent. 


Cost of binder per ton 
of briquets, cents 


Petroleum residuum 


4 

5 to 6 
6.5 to 8 


45 to 60 


Water-gas tar pitch 


50 to 60 


Coal-tar pitch. 


65 to 90 







Many other binders have been used, but as a rule with less success or 
at greater cost. The cost of petroleum residuum is much higher now 
(1916) than when the report of the Bureau of Mines was made. 

Lignite and peat briquets have been made with the use of no addi- 
tional binder, but to date (1916) not on an extended commercial basis 
in the United States. 

Briquets of 65 per cent, sawdust and 25 per cent, coal dust have been 
made with binders of coal-tar, pitch, petroleum refuse or sulphite waste 
liquor. 

AVERAGE HEATING VALUES OF SOLID FUELS 

Although average values are often misleading, if properly used the 
following table of the average of a large number of determinations of the 
heating value of fuels may be of service. Unless otherwise specified the 
values are B.t.u. per pound of dry fuel. 

B.t.u. per pound 

Anthracite 11,500-14,000 

Semi -anthracite 13,000 

vSemi-bituminous coal . 14,000-15,000 

Bituminous coal 11,000-14,000 

Lignite (as fired) 8,300 

Lignite (dry) •. 11,300 

Coke 12,000 

Charcoal 11,600-13,500 

Peat (as fired) 4,000- 8,000 

Peat (dry) 5,000-10,000 

Wood (dry) 6,600- 9,900 

Bagass (45 to 55 per cent, water) 3,000- 3,500 

Tan bark (65 per cent, water) 2,700 

Tan bark (dry) 6,000- 9,500 

Straw ; 5,100- 6,700 



FUELS 375 

Weight and Volume of Coals. — 

One ton (2,000 lb.) Approximate space 

of required, cu. ft. ' 

Anthracite lump 28 . 8 

Anthracite broken 30 . 3 

Anthracite egg '. 30 . 8 

Anthracite stove. 31 . 1 

Anthracite chestnut 31.9 

Anthracite pea. 32 . 8 

Max. Avg. Min. 

Bituminous coal 45 . 6 37 . 8 34 . 3 

The weight of a 

bushel of coal, 

pounds 

In Indiana 70 

In Pennsylvania 76 

In Alabama, Colorado, Georgia, Illinois, Ohio, Tennessee and 

West Virginia 80 

Weight of a bushel of coke, pounds 
Maxinxum Average Minimum 

- 50 40 33 

When buying coal it is well to remember that : 1. The heating power 
per pound of combustible is about constant; and more attention should 
be paid to the per cent, of earthy matter than to the calorific value per 
pound of coal. 

2. The earthy matter appears to increase by about 13^-2 per cent, for 
each size of coal as it becomes smaller, but the price often diminished in 
a greater ratio. 

3. The amount of refuse is always much in excess of the earthy matter 
reported by analysis. 

4. With anthracite, the best qualities are indicated by the sharpest 
angles and the brightest appearance. If the coal is dull and shows seams 
and cracks, it will split up in the fire and not prove economical. 

5. Bituminous coals showing whitish films or rusty stains should be 
avoided, as they indicate the presence of sulphur and pyrites. 

The Purchase of Coal under Government and Commercial Specifica- 
tions on the Basis of its Heating Value. — Until recent years, coal consum- 
ers purchased coal merely on the statement of the dealer as to its quality, 
relying on his integrity and on the reputation of the mine or district from 
which the coal was obtained. Even today this method must be followed 
by small consumers, by local dealers and even by some fairly large con- 
sumers. Only the Government and very large consumers, or a combina- 
tion of small consumers, can afford to buy by specification at the present 
time. 



376 ENGINEERING OF POWER PLANTS 

The purchase of coal by specification is an important step toward the 
conservation of our national mineral resources, for it results in an in- 
creased use of the lower grades of coal. The poorer coals find a market 
by competing with the better grades, not as to the price per ton but as 
to the cost of an equal number of heat units. 

Factors Affecting Value. — -Some of the factors that may influence the 
commercial results obtained in a boiler are cost of the coal as determined 
by price and heating value, care in firing, design of the furnace and boiler 
setting, size of grate, formation of excessive amounts of clinker and ash, 
available draft and size of coal. 

Of the. physical characterisitcs of coal the following have a direct 
bearing on the value as a power-plant fuel: 

(a) Moisture. 

(6) Ash. 

(c) Volatile matter and fixed carbon. 

(d) Sulphur and clinker. 

(e) Size of coal. 
(/) Heat units. 

(a) Moisture in the coal is worthless, costs money for freight and cart- 
age and loss of heat. 

(b) Non-combustible material, called ash, is worthless to the pur- 
chaser. In commercial coals this proportion of ash ranges from 4 to 25 
per cent. As a rule the higher the percentage of ash, the poorer the coal. 
A fusible ash may be a very serious matter. 

(c) Although furnaces designed for high- volatile coals may give results 
that make the coal as desirable as one low in volatile matter, yet in gen- 
eral the coal containing the higher percentage of fixed carbon is more 
efficiently handled or ''burns better.'' 

(d) Sulphur in the free state gives little trouble, but if combined with 
iron and other impurities may seriously reduce the efficiency of a furnace. 
Iron sulphide usually makes a fusible ash and causes clinker troubles and 
excessive grate-bar renewals. 

(e) For efficient furnace results, coal should be fairly uniform in size. 
Very fine coals or coal dust, tend to check the draft and usually require 
special furnace construction. It is important to know the caking quali- 
ties of coal. 

(/) In general the efficiency and value of coals will vary directly witn 
the B.t.u. value, but as indicated above, the character of the ash and the 
form of the sulphur present, may destroy this relation. Suitable furnace 
construction is also an important factor. 

In general, then, considerable care must be exercised in purchasing 
coal to meet properly the requirements imposed by local plant conditions 
as to character and variation of load,- type of furnace, etc. 



FUELS 377 

Specification Standards. — Kent^ summarizes the standards as follows: 
*^ Anthracite and Semi-anthracite. — The standard is a coal containing 

5 per cent, volatile matter, not over 2 per cent, moisture, and not over 
10 per cent. ash. A premium of 0.5 per cent, on the price will be given 
for each per cent, of volatile matter above 5 per cent, up to and including 
15 per cent., and a reduction of 2 per cent, on the price will be made for 
each 1 per cent, of moisture and ash above the standard. 

Semi-bituminous and Bituminous. — The standard is a semi-bituminous 
coal containing not over 20 per cent, volatile matter, 2 per cent, moisture; 

6 per cent. ash. A reduction of 1 per cent, in the price will be made for 
each 1 per cent, of volatile matter in excess of 25 per cent., and of 2 per 
cent, for each 1 per cent, of ash and moisture in excess of the standard. 

For Western coals in which the volatile matter differs greatly in its 
percentage of oxygen, the above specification based on proximate analysis 
may not be sufficiently accurate, and it is well to introduce either the 
heating value as determined by a calorimeter or the percentage of oxygen. 
The author has proposed the following for Illinois coal: 

The standard is a coal containing not over 6 per cent, moisture and 
10 per cent, ash in an air-dried sample, and whose heating value is 14,500 
B.t.u. per pound of combustible. For lower heating value per pound of 
the combustible, the price shall be reduced proportionately, and for each 
1 per cent, increase in ash or moisture above the specified figures, 2 per 
cent, of the price shall be deducted." 

The United States Government has been purchasing coal under 
specification for some years. The essential points of the Government 
specifications are as follows: 

BITUMINOUS COAL 

Description of Coal Desired 

1. The coal must be a good coal and must be adapted for successful use in 
the particular furnace and boiler equipment. 

2. Bidders are required to specify the coal offered in terms of moisture, 
"as received;" ash, volatile matter, sulphur, and British thermal units, "dry 
coal." Such values become the standards for the coal of the successful bidder. 
In addition the bidders are required to give the trade name of the coal offered, the 
name or other designation of coal bed, name of mine or mines, location of mine 
or mines (town, county, and State), railroad on which mine or mines are located, 
and name of operator of mine or mines. 

Note. — Bids not supplying the foregoing information may be considered informal 
and rejected. Coal of the description and analysis specified is herein known as the 
contract grade. Bidders are cautioned against specifying higher standards than 

1 " Mechanical Engineers' Pocketbook," 9th edition, p. 830. 



378 ENGINEERING OF POWER PLANTS 

can be maintained, for to do so will result in deductions in price and may result in the 
rejection of delivered coal or cancellation of the contract. In this connection it should 
be recognized that the small "mine samples" usually indicate a coal of higher economic 
value than that actually delivered in carload lots because of the care taken to separate 
extraneous matter from the coal in the ''mine samples." 

Award 

3. In determining the award of this contract, consideration will be given to 
the quality of the coal (expressed in terms of ash in ''dry coal," of moisture in 
coal ''as received," and British thermal units in ''dry coal") offered by the 
respective bidders, to the operating results obtained on the same and similar 
coals on previous contracts or by test, as well as to the price per ton. 

4. Bids may be rejected from further consideration if they offer coals regard- 
ing which the Government has information that they possess unsuitable physical 
characteristics or excess volatile matter or sulphur or ash contents, or that they 
are unsatisfactory because of clinkering or excessive refuse, or because of having 
failed to meet the requirements of city smoke ordinances, or for other cause that 
would indicate that they are of a character or quality that the Government 
considers unsuited for use in its storage space or in its power-plant furnace 
equipment. 

5. In order to compare bids as to the quality of the coal offered all proposals 
shall be adjusted to a common basis. The method used shall be to merge the 
four variables — ash, moisture, heating value, and price bid per ton — into one 
figure, the cost of 1,000,000 B.t.u., so that one bid may readily be compared with 
another. The procedure under this method will be as follows : ' 

(a) All bids shall be reduced to a common basis with respect to moisture by 
dividing the price quoted in each- bid by the difference between 100 per cent, and 
the percentage of moisture guaranteed in the bid. The adjusted bids shall be 
figured to the nearest tenth of a cent. 

(6) The bids shall be adjusted to the same ash percentage by selecting %s the 
standard the proposal that offers coal containing the lowest percentage or ash. 
The difference in ash content between any given bid and i}his standard shall be 
divided by 2 and the price in such bid, adjusted in accordance with the above, 
multiplied by the quotient. The result shall be added to the above adjusted 
price. The adjusted bids shall be figured to the nearest tenth of a cent. 

(c) On the basis of the adjusted price, allowance shall then be made for the 
varying heat values by computing the cost of 1,000,000 B.t.u. for each coal offered. 
This determination shall be made by multiplying the price per ton adjusted for 
ash and moisture contents by 1,000,000 and dividing the result by the product of 
2,000, multiplied by the number of British thermal units guaranteed. 

6. After the elimination of undesirable bids the selection of the lowest bid 
of the remaining bids on the basis of the cost per 1,000,000 B.t.u. may be con- 
sidered by the Government as a tentative award only, the Government reserving 
the right to have practical service test or tests made under the direction of the 
Bureau of Mines, the results to determine the final award of contract. The 
interested bidder or his authorized representative may be present at such test. 



i 



FUELS 379 



Causes for Rejection 



7. It is understood that coal containing 3 per cent, more moisture, or 4 per 
cent, more ash, or 3 per cent, more volatile matter, or 1 per cent, more sulphur, 
or 4 per cent, less British thermal units than the specified guarantees as the 
standards for the coal hereunder contracted for, or if coal is furnished from mine 
or mines other than herein specified by the contractor, unless upon the written 
permission of the Government, shall be considered subject to rejection, and the 
Government may, at its option, either accept or reject the same. Should the 
Government have used a part of such coal subject to rejection, such shall not 
impair the Government's right to cause the contractor to remove the coal remain- 
ing of the delivery subject to rejection. 

8. It is agreed that if the contractor furnishes coal in three consecutive 
deliveries, or in case more than 20 per cent, of the amount of the coal delivered to 
any date during the life of this contract which contains 3 per cent, more moisture, 
or 2 per cent, more ash, or 3 per cent, more volatile matter, or 1 per cent, more 
sulphur, or 2 per cent, less British thermal units than the specified guarantees as 
the standards for the coal hereunder contracted for, or if coal is furnished from 
mine or mines other than herein specified, unless upon the written permission of 
the Government, then this contract may, at the option of the Government, be 
terminated, or the Government may, at its option, purchase coal in the open 
market until it may become satisfied that the contractor can furnish coal equal 
to the standards guaranteed, and the Government shall have the right to charge 
against the contractor any excess in price of coal so purchased over the corrected 
price which would have been paid to the contractor had the coal been delivered 
by him. 

9. The contractor shall be required to remove, without cost to the Govern- 
ment, within a reasonable time after notification, coal which has been rejected 
by the Government. Should the contractor not remove rejected coal within the 
said reasonable time, the Government shall then be at liberty to have the said 
coal removed from its premises and charge any and all costs incidental to its 
removal against the account of the contractor and to deduct the cost thereof from 
any money then due or thereafter to become due to the contractor. 

Price and Payment 

10. The Government hereby agrees to pay the contractor within 30 days 
after the completion of an order or delivery for each ton of 2,000 lb. of coal 
delivered and accepted in accordance with all the terms of this contract the price 
per ton determined by taking the analysis of the sample, or the average of the 
analyses of the samples if more than one sample is analyzed, collected from the 
coal delivered upon the basis of the price herein named adjusted as follows for 
variations in heating value, ash, and moisture from the standards guaranteed 
herein by the contractor. 

{a) Considering the coal on a ''dry-coal" basis, no adjustment in price shall 
be made for variations of 2 per cent, or less in the number of British thermal 
units from the guaranteed standard. When the variation in heat units exceeds 
2 per cent, of the guaranteed standard, the adjustment shall be proportional and 
shall be determined by the following formula: 



380 ENGINEERING OF POWER PLANTS 

B.t.u. delivered coal (''dry-coal" basis) . _ . i - f 

B.t.u. ("dry-coal" basis) specified in contract 
B.t.u. variation from the standard. 

The adjusted price shall be figured to the nearest tenth of a cent. 

As an example, for coal delivered on a contract guaranteeing 14,000 B.t.u. on 
a "dry-coal" basis at a bid price of $3 per ton showing by calorific test results 
varying between 13,720 and 14,280 B.t.u., there would be no price adjustment. 
If, however, by way of further example, the delivered coal shows by calorific test 
14,350 B.t.u. on a "dry-coal" basis, the price for this variation from the contract 
guaranty would be, by substitution in the formula: 

fig X $3 = $3,075. 

(6) No adjustment in price shall be made for variations of 2 per cent, or less 
below or above the guaranteed percentage of ash on the "dry-coal" basis. When 
the variation exceeds 2 per cent, the adjustment in price shall be determined as 
follows : 

The difference between the ash content by analysis and the ash content guar- 
anteed shall be divided by 2 and the quotient shall be multiplied by the bid price, 
and the result shall be added to or deducted from the British thermal units 
adjusted price or the bid price, if there is no British thermal unit adjustment, 
according to whether the ash content by analysis is below or above the percentage 
guaranteed. The adjustment for ash content shall be figured to the nearest 
tenth of a cent. 

As an example of the method of determining the adjustment in cents per ton 
for coal containing an ash content varying by more than 2 per cent, from the 
standard, consider that coal for which the above-mentioned heat-unit adjust- 
ment is to be made has been delivered on a contract guaranteeing 10 per cent, 
ash and shows by analysis an ash content of 7.50 per cent, the adjustment in 
price would be determined as follows: 

The difference between 10 and 7.50, which is 2.50, would be divided by 2, and 
the quotient of 1.25 multiplied by $3, resulting in an adjustment of 3.7 cts. per 
ton, which in this case would be an addition. The price after adjustment for the 
variations in heating value and ash content would be $3,075 plus $0,037, or $3,112. 

(c) The price shall be further adjusted for moisture content in excess of the 
amount guaranteed by the contractor, the deduction being determined by mul- 
tiplying the price bid by the percentage of moisture in excess of the amount 
guaranteed. The deduction shall be figured to the nearest tenth of a cent. 

As an example, consider the coal for which the above-mentioned heat unit 
and ash adjustments are to be made, and as having been delivered on a contract 
guaranteeing 3 per cent, moisture, and that the coal shows by analysis 4.58 per 
cent, moisture, then the bid price would be multiplied by 1.58 (representing excess 
moisture), giving 4.7 cts. as the deduction per ton. The price to be paid per ton 
for the coal would then be $3,112, less $0,047, or $3,065. 

11. If coal on visual inspection by the officer in charge appears to meet the 
contractor's guarantees, the said officer will have the right, immediately on the 
completion of an order, to make payment on 90 per cent, of the amount of the 
bill, based on the tonnage delivered and at the bid price per ton. The 10 per 



FUELS 381 

cent, withheld is to cover any deduction on account of the delivery of coal which 
on analysis and test is subject to an adjustment in price. If the 10 per cent, 
withheld should not be sufficient to cover the deduction, then the amount due the 
Government may be taken from any money thereafter to become due to the 
contractor, or may be collected from the sureties. 

Sampling 

12. The contractor shall have the privilege of having a representative present 
to witness the collection and preparation of the samples to be forwarded to the 
laboratory. 

13. The samples shall be collected and prepared in accordance with the 
method given in Appendix A, attached hereto as a part of these specifications 
and proposals. 

Analyses 

14. The samples shall be immediately forwarded to the Bureau of Mines, 
Department of the Interior, Washington, D. C, and they shall be analyzed and 
tested in accordance with the method recommended by the American Chemical 
Society and by the use of a bomb calorimeter. The expense of such analyses and 
tests shall be made at no cost to the contractor. The results shall be reported 
by the Bureau of Mines to the officer in charge in not more than fifteen (15) days 
after the receipt of the sample — if more than one sample is received from the 
same delivery, the fifteen (15) days shall date from the receipt of the last sample 
taken. 

Method of Sampling. — Proper sampling of coal is diflScult. So much 
depends upon it that it must be properly done. For instructions in this 
field, the student is referred to the Bulletins of the Bureau of Mines and 
to the reports of Committee D-5, A. S. T. M. (1916). 

Use of Briquets. — Briquets are good fuel. The only drawback is the 
cost of the binder, as it usually does not pay to briquet if the binder costs 
more than 25 cts. per ton of briquets. 

An elaborate and carefully executed series of tests involving the use 
of natural coals and of briquets made from the same coal, previously 
crushed, has been carried out on a locomotive mounted at the testing 
plant of the Pennsylvania Railroad Co. at Altoona, Pa., under the direc- 
tion of the Government Testing Station. Less extensive tests were made 
on several other railroads and some prehminary experiments involving 
the use of briquets in marine service have beeii made in connection with 
one of the Government's torpedo boats. 

Results of Experiments. — The results obtained in these tests are said 
to sustain the following general conclusions: 

1. The briquets made on the Government's machines have well with- 
stood exposure to the weather and have suffered but little deterioration 
from handling. 



382 ENGINEERING OF POWER PLANTS 

2. In all classes of service involved by the experiments the use of 
briquets in place of natural coal appears to have increased the evaporative 
efficiency of the boilers tested. 

3. The smoke produced has in no test been more dense with the bri- 
quets than with coal; on the contrary, in most tests the smoke density is 
said to have been less when briquets were used. 

4. The use of briquets increases the facihty with which an even fire 
over the whole area of the grate may be maintained. 

5. In locomotive service the substitution of briquets for coal has re- 
sulted in a marked increase in efficiency, in an increase in boiler capacity, 
and in a decrease in the production of smoke. It has been specially 
noted that careful firing of briquets at terminals is effective in diminishing 
the amount of smoke produced. 

General Deductions. — At the usual rate of combustion in locomotives 
the equivalent evaporation with either kind of briquet is 10 to 15 per cent, 
higher than with run-of-mine coal. 

So far as blackness of smoke is concerned there seems to be little ad- 
vantage in briquets over run-of-mine coal. However, the loss in sparks 
is less, and especially with the larger size of briquets. 

It is a great deal easier to raise and to keep up steam with briquets 
than with run-of-mine coal as they contain no fines. Higher rates of 
combustion are feasible and consequently higher power, which is of espe- 
cially great advantage on long grades. 

As to efficiency, there is practically no difference between the two 
sizes of briquets, but the smaller ones are easier to handle. 

Torpedo-boat Service.— In torpedo-boat service the substitution of 
briquets for coal improves the evaporative efficiency of the boiler. It 
does not appear to have affected, favorably or otherwise, the amount of 
smoke produced. 

Steam can be raised more quickly with briquets than with run-of- 
mine coal. 

Run-of-mine coal is transferred much more readily than briquet 
from the coal bunker to the fire room. With briquets the capacity of a 
coal bunker is reduced by 23 to 27 per cent. 

Use of Low-grade Fuels. — The Reports of the U. S. Geological Survey 
show that, if the rate of increase of fuel consumption in this country that 
has held for the past 50 year is maintained, the supply of easily available 
coal will be exhausted within a very few hundred years— some say 
within two hundred. As is shown in Fig. 214, the annual production of 
coal in the United States increased from 20,000,000 tons 60 years ago 
to nearly 640,000,000 tons in 1917; if the industries of the country con- 
tinue to develop at a sufficient pace to maintain this rate of increase, 
then the limit of our coal supply will" be reached in about 200 years. 



FUELS, 



383 



The fuel consumption per capita is actually increasing much faster than 
the population, so that the question of the continuation of this rate of 
increase is one of considerable importance. 

A serious situation confronts us when we realize that our really high- 
grade coals — the semi-bituminous and anthracite of the eastern provinces 



1307-1817 
1318-1827 
1328-1837 
1338-1847 
1848-1857 
1858-1837 
1868-1877 
1878-1837 
1838-1897 
1398-1907 
1903-1917 



L 



Tons of 2000 Lbs, 
1,000 
65,000 
608,000 



3,100,000 
10,000,000 



20,700,000 
47,300,000 



97,800,000 
173.000,000 



640,000,000 



Fig. 214. — Average annual production of coal in the United States by decades from 
1807 to close of 1917. (Ill years.) 



— amount to less than one-seventh (or about 15 per cent.) of the avail- 
able coal reserves of the country. 

Approximately an additional 15 per cent, may be classed as coal of 
medium grade, but the bulk of our coal — 70 per cent, of the entire 
supply — consists of low-grade bituminous coal and lignite. 



Year 

1870 



1890 
1900 
1915 



t Tons 
0.96 


Percent 
Increase 


1.4 


45.8 


2.3 


64.1 


3.2 


39.1 


5.5 


71.9 



Fig. 215. — Per capita coal consumption in the United States. 



It is perhaps well to conect a rather general impression that anthra- 
cite is the highest grade fuel. As a matter of fact, our semi-bituminous 
coals rank first, as shown by the following table of comparative heating 
values per pound of combustible material: 



384 ENGINEERING OF POWER PLANTS 

B.t.u. per lb. 
(ash free) 

Semi-bituminous 15,420 

Anthracite and semi-anthracite 14,660 

Bituminous 13,970 

Sub-bituminous and lignite , 8,560 

The exhaustion of these semi-bituminous coals would be a far greater 
calamity than the exhaustion of the anthracite supply, as they are much 
better adapted for general commercial purposes and are more efficient 
than anthracite, the latter being used but little outside of the domestic 
field. 

It is interesting to note that the production of coal in the United 
States has been for some years greater than that in any other country. 
The world's production of coal by countries is given in Fig. 205. 

Investigations into the waste of coal in mining have shown the enor- 
mous extent of this waste, aggregating from 200,000,000 to 300,000,000 
tons yearly, of which at least one-half might be saved. Attention is 
being directed to the practicability of reducing this waste through more 
efficient mining methods. It has also been demonstrated that the low- 
grade coals high in sulphur and ash now being left underground can be 
used economically in the gas producer for power and light, and should, 
therefore, be mined at the same time that the high-grade coal is removed. 

The following low-grade fuels should, therefore, receive thoughtful 
consideration : 

1. High-ash fuels, which are regarded at present as practically worth- 
less. 

2. Extensive deposits of lignite found in various sections of the 
country. 

3. Peat from vast areas of swamps and bogs. 

A study of the situation leads to the belief that the utilization of these 
fuels, which have until recently been regarded as of little or no value, 
may increase the fuel resources of the United States approximately (on 
the basis of present marketable grades) : 

Per cent. 

(a) Low-grade bituminous and anthracite 75 to 100 

(b) Sub-bituminous, hgnite and peat 60 

or roughly, a total of 150 per cent. 

In considering the use of such fuels, it must not be overlooked that 
the percentage of ash is high in the low-grade bituminous and anthracite 
fuels and the percentage of moisture high in many of the lignites and in 
the peats. These conditions practically prohibit transportation and 
necessitate the use of these grades in close proximity to the mine or bog. 

Powdered Fuel. — The use of pulverized coal for steam generation 
is becoming increasingly important. Much of the data presented is 



FUELS 



385 



COUNTRY 



' United States 

(1913) 

Great Britain 

(1913) 

Germany 

(1912) 

Austria- Hungary 

(1912) 

France 

(1913) 
Russia 

(1912) 
Belgium 

(1912) 

Japan 

(1912) 

China 

(1912) 

India 

(1912) 
Canada 

(1913) 
New South Wales 

(1913) 

Spain 

(1912) 
Transvaal 

(1911) 

Natal 

(1911) 
New Zealand 

(1912) 

Holland 

(1912) 

Queensland and 

Victoria 

(1912) 

Chile 

(1912.) 

Asiatic Russia 

(1910) 

Mexico 

(1912) 
Bosnia and Herze 

govina 

(1912) 
Turkey 

(1912) 

Italy 

(1912) 
Dutch East Indies 

(1912) 

Sweden 
(1912) 

Other Countries 



SHORT TONS 



100,000,000 200.000.000 300.000,000 400,000.000 500.000.000 600.000.000 




397,149 
3.847,202 



Fig. 216. — World's, production of coal. 



386 ENGINEERING OF POWER PLANTS 

from a topical discussion before the American Society of Mechanical 
Engineers. 

1. Necessity for drying coal before grinding: 

Coal should be dried to 1 per cent, or less moisture. Moisture is 
objectionable because 

(a) it reduces capacity of grinders; 

(&) it tends to pack in storage bins and burners; 

(c) it lowers possible attainable temperatures; 

(d) it lessens efficiency. 

2. Fineness of grinding: 
Standard practice is 

95 per cent, through 100 mesh screen. 
80-85 per cent, through 200 mesh screen. 

3. Cost of grinding and handling, including upkeep. 

These items vary considerably especially under different operating 
conditions. A brief summary of the reported costs for five plants is as 
follows: 

For Plant (A) About 45 cents per ton 

Cents 

Labor. 15 . 

Power : 10. 

Repairs 14.5 

Coal for drying. 5.5 

45.0 
For Plant (B) Based on 200 tons in 24 hours. 

Cost of grinding, 
handling, etc., 
Price of coal per ton, cents 

$1 17.6 

2 21.8 

3 23.9 
Not including overhead charges, interest or depreciation. 

For Plant (C) For 150 tons per day, 40 cents per ton. 

For Plant (D) For 140 tons per 24 hours in plant built 16 years ago 

Cost per 
ton, cents 

Labor, operating 15 . 64 

Labor, repairs 1 . 70 

Supplies, fuel, power, etc 14 . 71 

Oil and waste 1-25 

Repairs 4 . 54 

37.84 
Interest, depreciation and obsolescence 1 . 35 

39.19 

For Plant (E) From 11.4 cents per ton to 49.2 cents depending upon the degree of 
pulverization, amount of coal consumed, etc. 



FUELS 



387 



4. Danger from particles of dust floating in the air. 

Experience indicates that there is no danger from powdered fuel 
except when fine dust floats in the air. When this is the condition, 
there is danger of spontaneous combustion. Dampening the dust 
with sprinklers should prevent such danger. If floating dust is present, 
the following precautions should be taken: (a) permit no smoking; 
(h) prohibit the use of matches; (c) prohibit the use of naked gas lights; 
Id) avoid places for lodging of dust; (e) prevent the escape of dust. 

In Fig. 216a is shown a furnace design for burning low volatile, high 
fixed carbon fuels, such as anthracite, coke breeze, etc. 




Fig. 216a. — Design of furnace for burning low-volatile, high fixed-carbon fuels. 

H. G. Branhurst says: "In these furnaces the blast passes down and 
up and over an arch, thereby surrounding the incoming fuel and supply- 
ing the heat necessary for the initial ignition. The main principle 
governing the design of a furnace for burning pulverized coal is that it 
must be sufficiently large so .that the coal when burned will have time 
to complete its combustion before leaving the furnace. In open hearth 
furnace practice the same condition exists as in rotary kilns, i.e., the fuel 
must be projected and burned directly over the bath. Furnaces to 



388 ENGINEERING OF POWER PLANTS 

suit fuel requirements for any individual operation should be designed 
especially for the work in question." 

W. A. Evans states that aside from building combustion space large 
enough and of maintaining combustion, there is little chance for powdered 
coal coming into general use on water tube boilers. The cost of grinding 
eats up any possible small advantage in economy it might have over 
the very efficient operation of mechanical stokers. The 95 to 97 per cent, 
furnace efficiency of the latter leaves a very narrow margin for im- 
provement; certainly not as much as 40 cents, the cost of grinding each 
'ton of coal. That leaves the field for powdered fuel boiler firing possibly 
to horizontal return tubular boilers and to a few special conditions, such 
as waste fuel or a fuel that cannot be burned on stokers. The writer 
suggests a use that, to his knowledge, has not been tried. It is for 
peak loads. Powdered coal used only to supply the peak loads to 
heavily overloaded boilers would very much increase their capacity, 
would be in use only for short periods, would be entirely automatic, and 
might prove of untold values. 

His experience has been that wherever ash has a chance to deposit 
within the range of the flame slag will form and be of such a sticky, 
sluggish nature that it is next to impossible to remove it. It chills sohd 
at 1800°, or as soon as any door is opened to break it out. It is suggested 
that a flux be used to make the slag more fluid, so as to allow it to be 
drawn off in its fluid state. 

F. P. Coffin^ says: ''Coal can be pulverized more cheaply than it 
can be gasified and the first cost of a plant for drying and pulverizing is 
less than for a producer-gas plant. When thoroughly mixed with a 
blast of air in correct proportion, it is practically a gaseous fuel. Pow- 
dered coal firing has most of the advantages of gas or oil firing for steam 
boilers, when properly applied, and in industrial heating its field of 
application is constantly growing. 

''The principal difficulty is in connection with the ash produced in 
the flame. This is often the feature which limits the practicability of 
powdered coal firing for industrial furnaces." 

Other writers claim that there is little trouble from ash or slag in 
furnaces operating at temperatures above 2,000°F. 

The air pressure for blowing the coal into the furnace averages from 
4 to 9 ounces. 

The stack draft should be strong enough to take care of the products 
of combustion and sufficient to create a slight vacuum in the furnace 
to prevent outward leakage. 

The life of furnaces using powdered coal seems about the same as 
when using oil. 

1 General Electric Review 1917, page 616. 



FUELS 389 

John Anderson presents^ a very complete summary of results from 
tests of fuel pulverizing equipment as applied to power plants as follows: 

SUMMARY SHEET 

Electric Energy and Fuel Consumption per Ton of Coal Pulverized 

I. Energy consumed by conveyors, crushers, elevators, dryer, blowers and 

feeders, kw.-hr 5 . 73 

2. Energy consumed by pulverizer, kw.-hr 16. 72 

3. Total energy, kw.-hr 22 . 45 

4. Coal equivalent at 1.5 lb. per kw.-hr., lb 33 . 68 

5. Coal consumed in dryer furnace, lb. per ton of fuel dried 25 . 66 

6. Total coal and equivalent, lb 59 . 34 

7. Gross efficiency less deductions for toal coal and equivalent — Item 6. . . . 78.36 

Cost of Fuel Preparation, Firing and Ash Disposal 

8. Labor — coal preparation . $0. 143 

9. Labor — firing . 112 

10. Labor — ash removal . 025 

II. Dryer fuel — coal at $4.00 per ton . 051 

12. Electric energy — coal per kw.-hr. at 1.5 lb 0. 068 

13. Maintenance (labor at 3.6c. — material at 2.0c. manufacturer's estimate — 

lubricants at 0.7c.) 0. 063 

14. Total cost of fuel preparation, firing, ash disposal and maintenance 0.462 

15. Price of coal as purchased, per ton. , 4.000 

16. Total cost 4.462 

Efficiencies 

17. Actual gross efficiency, per cent 80. 67 

18. Net efficiency after all incidental costs have been accounted for, per cent. 72.32 

CONCLUSIONS 

The conclusions can be best drawn from a comparison between pulverized fuel 
burning equipment and mechanical stokers. 

Comparison of Costs and Net Efficiencies 
Electric Energy and Fuel Consumption per Ton of Coal Burned 

Pulv. fuel Modern 

System Stoker 

Energy consumed by conveyors, crusher, ele- Stokers and 

vators, dryers, fans and feeders, kw.-hr 5 . 73 blowers, kw.-hr, 10 . 94 

Energy consumed by pulverizer, kw.-hr 16. 72 

Total energy, kw.-hr 22. 45 10. 94 

Coal equivalent at 1.5 lb. per kw.-hr., lb 33.68 16.41 

Coal consumed in dryer furnace, lb 25.66 

Total cost and equivalent, lb 59 . 34 16.41 

1 "Use of Pulverized Coal Under Central Station Boilers," by John Anderson, 
Chief Engineer of Power Plants of the Milwaukee E. R. & L. Co. 



390 ENGINEERING OF POWER PLANTS 

Cost of Fuel Preparation, Firing and Ash Disposal 

Labor — coal preparation $0. 143 $0. 000 

Labor — firing 0. 112 0. 140 

Labor — ash removal (in plant) . 025 . 064 

Dryer fuel— coal at $4.00 per ton . 051 . 000 

Electric energy — coal per kw.-hr. at 1.5 lb 0.068 0.033 

Maintenance : 

Labor at $0,046 

Labor at $0.036— (material at $0,020 manu- Material at $0,049 

facturer's estimate — lubricants at $0.007... . 0.063 Lubricants at $0,002 0.007 

Total cost. of fuel preparation, firing, ash dis- 
posal and maintenance . 462 . 334 

Price of coal as purchased, per ton 4 . 000 4 . 000 

Total cost, per ton 4 . 462 4. 334 

Cost per ton of coal in P. F. system over modern 

stoker 0.128 



EFFICIENCY 

Actual gross efficiency, per cent .. 80.67 76.80 

Net efficiency after all incidental costs have 

been accounted for, per cent 72.32 70.88 

Difference in favor of pulverized fuel system, 

per cent 1 . 44 ..... 



Liquid Fuels. — The liquid fuels which are used on a large enough 
scale to warrant consideration as power-plant fuels are: fuel oil, gasoline, 
kerosene and alcohol. 

The heating values and weights of these fuels run about as follows: 



Pounds per 

gallon B.t.u. per pound 

Fuel oil 8.3 to 6.7 18,400 to 20,400 

Gasoline (high-grade) 6.0 20,500 

Gasoline (0.710 sp.gr.) 18,500 

Kerosene (0.863 sp. gr.) 18,700 

Kerosene 6.6 19,900 

Denatured alcohol 6.8 11,600 



With the possible exception of denatured alcohol these fuels need no 
definition. Denatured alcohol as used for power purposes consists of 
grain alcohol (C2H6O) made poisonous and repulsive by the addition of 
wood alcohol and benzine in the following proportions: 100 parts grain 
alcohol; 10 parts wood alcohol, H P^-it benzine. 



FUELS 391 

B. S. Nelson 1 reports that Spindle Top oil (Texas) has a specific 
gravity of about 0.92, corresponding to 22°Be., and its heat value averages 
about 19,700 B.t.u. California oil is somewhat heavier, the average 
grade of that oil having a specific gravity of about 0.95, or 18°Be., heat 
value about 18,500 B.t.u. The Mexican oils vary considerably in 
specific gravity and heat value, but as a rule they are much heavier than 
either the California or Texas oils; a typical oil now used has 0.99 sp. gr., 
or 12°Be., with a heat value of about 18,200 B.t.u. 

WORLDS' PRODUCTION OF PETROLEUM 

The position of the United States in relation to the world's pro- 
duction of petroleum is even more marked than its relation to the world's 
production of coal, nearly two-thirds of the total annual production of 
petroleum coming from this country as shown in Fig. 217, 



Barrels of Percentage 
Country 42 Gallons of Total 

300,800,000 



United States 

_ ^^^^^ 72,800,000 15 

39,800,000 8 



Mexico 

Dutcb East Indies 

Boumania 

India 

Galicia 




65,29 



13,200,000 2.86 

10,100,000 2.24 

8.200,000 1.79 

6.400,000 1.40 

. 3.000.000 .65 
Japan end Formosar 2.600.000 

^^'^ ' 1.000,000 .22 

1,000.000 .23 

^^'•""^y 870.000 

Argentina f 

.„ .u r. . = 600,000 .14 
All other Cuuntriesi 

Fig. 217. — World's production of petroleum in 1916. 



From the beginning of the petroleum industry in the United States 
to the close of 1917 this country produced approximately 4,250,000,000 
bbl., or about 60 per cent, of the entire production of the world for this 
period . 

According to most careful estimates of the United States Geological 
Survey, the probable total original petroleum resources of the country 
amounted to over 11,000,000,000 bbl., of which the exhaustion to the 
close of 1915 amounted to over 3,600,000,000 bbl., leaving for possible 
future production about 68 per cent, of the original supply, or some 
7,600,000,000 bbl. 

If we assume a lake 100 ft. deep and 1 mile wide, the length of the 
lake corresponding to the estimated total original petroleum resources 

' ''Oil Burning," by B, S. Nelson, A.S.M.E. Journal, June, 1917. 



392 ENGINEERING OF POWER PLANTS 

would be over 22 miles. The exhaustion means that we have cut off 
more than 7 miles from the length of the lake and have left the equivalent 
of a lake 15 miles long, 1 mile wide, and 100 ft. deep. 

As in the case of the coal resources, the alarming point is the rapidly 
increasing rate of exhaustion, as shown by Fig. 218. 





Barrels 


59-1807 


I 2,200,000 


68-1877 


OV 7.700,000 


78-1887 


■"V 24,500,000 


88-1897 
98-1907 


"■■^■•^vs,^^^ 48,000,000 




08-1917 




1917 


344,200.000 





Fig. 218. — Average annual production of crude petroleum in the United States, by 

decades. 



On the basis of a future constant consumption equal annually to 
the estimated 1917 consumption of 344,177,000 bbl., the estimated 
available reserves of 7,629,000,000 bbl. would last only about twenty- 
two years, and with an increasing consumption rate per decade equal to 
from two to two and a half times the consumption for the preceding 
decade the depletion of our petroleum supply seems near at hand. 

However, just as we become alarmed at the rapid exhaustion of our 
petroleum resources, information appears which indicates that there 
are wor^derful mountains of oil-laden shales in the western states and 
similar shales in the east-central states, from which some 40 or 50 gal. 
of oil can be extracted per ton of shale. Similar processes have been 
carried on in Scotland for the past seventy years. The Colorado shales 
alone are estimated to contain some 20,000,000,000 to 30,000,000,000 
bbl. of oil, and for the Indiana shales estimates as high as 100,000,000,000 
bbl. of oil are reported. These figures indicate that our shale oil resources 
are enormously greater than our original petroleum resources. 

Oil versus Coal under Boilers. — Of these fuels the only one used on 
a commercial basis for steam generation in boilers is fuel oil. It is, there- 
fore, important to compare the relative results from coal and oil for this 
purpose. 

Kent gives^ the following table based on the assumed data: B.t.u. 
per pound of oil, 19,000; weight of oil, 7.57 lb. per gallon: 1 bbl. = 42 
gal. = 315 lb. 

1 '' Mechanical Engineers Pocketbook," 9th edition, p. 842. 



FUELS 



393 



Coal, B.t.u. per pound 


1 lb. oil = pounds 

coal 


1 bbl. oil = pounds 

coal 


1 ton coal = barrels 

oil 


10,000 


1.9 


598 


3.34 


11,000 


1.73 


544 


3.68 


12,000 


1.58 


499 


4.01 


13,000 


1.46 


460 


4.34 


14,000 


1.36 


427 


4.68 


15,000 


1.27 


399 


5.01 



This table shows that if coal of a heating value of only 10,000 B.t.u. 
per pound costs $3.34 per ton and coal of 14,000 B.t.u. per pound costs 
$4.68 per ton, then the price of oil will have to be as low as $1 per barrel 
to compete; or, on this basis oil will be the cheaper fuel if it is below $1 
per barrel. 

In general it may be said that the heating value of crude petroleum 
is from 1.44 to 1.6 times that of average good coal, even after deducting 
the steam used to operate the pulverizers, which steam amounts, to about 
4 per cent, of the total evaporation of the boilers. With the best types 
of apparatus this can be reduced to 2 per cent. 

Under exceptional conditions fuel oils may evaporate from 16 to 17 lb. 
of water from and at 212°F. per pound of oil. 

If the weight of a gallon of oil be 6.8 lb. and the cost per barrel (42 
gal.) be $0.94, then the cost of 2,000 lb. would be $6.58 and at a commer- 
cial efficiency of 1 to 1.6 the values of the fuels would be the same when 
coal delivered, including handling of ashes, costs $4.12. 

The boilers at the Chicago World's Fair gave the following average 
results : 



Consumption of oil per hour 22 . 792 lb. 

Equivalent evaporation per pound of oil from and at 212° . , 14. 88 lb. 

Cost of oil per hour $56 . 20 

Cost of oil per boiler horsepower-hour $0 . 0057 

Cost of labor per boiler horsepower-hour $0 . 0006 

Experiments on express locomotives in England gave 

1 lb. of oil (max.) was equivalent to 2.4 lb. coal. 
1 lb. of oil (min.) was equivalent to 2.0 lb. coal. 
1 lb. of oil (avg.) was equivalent to 2.2 lb. coal. 

With reference to the relative prices of coal and oil. Nelson gives the 
figures of Table 1. 



394 ENGINEERING OF POWER PLANTS 

Table 1. — Compari;5on of Prices of Coal and Oil 



Coal, dollars per ton, 
2,000 lb. 


Oil, dollars per bbl. 


5.00 


1.50^ 


1.662 


4.75 


1.43 


1.60 


4.50 


1.35 


1 . 50 


4.25 


1.28 


1.42 


4.00 


1.20 


1.33 


3.75 


1.13 


1.25 


3.50 


1.05 


1.02 


.3.25 


0.98 


1.01 


3.00 


0.90 


1.00 


2.75 


0.83 


0.92 


2.50 


0.75 


0.83 


2.25 


0.68 


0.75 


2.00 


0.60 


0.66 



^ Not allowing for labor saving. 

2 Assuming 10 per cent, of cost of fuel in labor of firing and handling ashes saved 
by using oil, a conservative estimate for plants of over 300 hp. 



He further says: ''Oil has numerous other advantages over coal than 
cost of fuel. The storage space required is much less for an equal number 
of heat units; there are no ashes to be disposed of; less boiler-room help 
is required for firing; the wear and tear on the furnace lining is smaller 
because the firedoors do not have to be opened, with the consequent 
chilling of the hot brickwork. Very little repairs are necessary to the 
grate bars; a much smaller stack can be used for the same boiler horse- 
power; the boiler can be forced with natural draft considerably beyond 
what it can with coal, an important feature where boiler capacity is 
scant; where feed water is bad, it is often possible to carry a load with 
two oil fired boilers which would require three boilers were coal used, 
thus allowing the cleaning and repairing of one dirty boiler at a time. 
Steam can be raised much more quickly and with, no loss due to banking 
fires. It takes about 10 per cent, of the fuel normally consumed by a 
boiler at rated load to keep its fire banked with coal. In case of an 
emergency the fire can be instantly extinguished ; anyone who has had to 
draw a hot coal fire in an emergency can appreciate this particular 
advantage." 

In a discussion of Mr. Nelson's paper, Mr. Snypp states that ''The 
requirements for successfully firing heavy crude oils seem to be, first, 
large pipe lines and slow moving, large capacity pumps; and second, 
proper preheating; third, superheated steam to atomize the oil." 



FUELS> 395 

The following figures are from tests^ of oil burning steam, electric 
power plants in Arizona. 

Plant A 

Rated load on boilers, per cent 100 80 60 125 

Boiler hp. developed 758 572 422 885 

Equivalent evaporation per lb. of oil. 15 . 62 15 . 73 16 . 00 15 . 34 

Efficiency of boiler, per cent ... 81.76 82.64 83.74 80.29 

Plant B 

Average load, kw 5,815 

Power factor. . 93 

Average gravity of oil 17 . 65 

Weight of oil per bbl. of 42 gal ; 332 

Heat value of oil, B.t.u. per lb 18,703 

Oil per kw.-hr., lb 0. 988 

Kw.-hr. per bbl. oil 336 

B.t.u. per kw.-hr 18,478 

Advantages of Liquid Fuel. — 

1. Reduction in number of firemen in proportion of 5 or 6 to 1. 

2. Easy lighting of fires and more regular supply of heat. 

3. Fires readily regulated to suit demand for steam, and can be 
promptly extinguished. 

4. Small proportion of refuse and its easy disposal. 

5. Storage tanks can be located to best advantage, while coal bins 
must be near the boilers. 

6. No sparks; no dust; no loss by banking. 

Disadvantage of Liquid Fuel. — 

1. Fire risk. Use prohibited by some city ordinances. 

2. Offensive odor. Use prohibited by some cities. 

3. Vapor forms explosive mixture with air. 

4. Supply limited. 

5. Burners make objectionable roaring noise. 

6. Heating surface apt to become coated with residue. 

7. Tendency of the oil to creep by valves and leak. 

8. Necessity for auxiliary apparatus to start oil fire or maintain it 
or both. 

Boiler Efficiency with Oil Fuel. — Although boiler efficiencies as high 
as 82 per cent, or above are reported with oil-burning furnaces, the aver- 
age is probably nearer 72 per cent, if the average with coal burning fur- 

1 "Economy of Arizona Power Plants Using Oil Fuel," by C. R. Weymouth, 
Mechanical Engineering, Jun©, 1919. 



396 ENGINEERING OF POWER PLANTS 

naces be taken as 70 per cent., i.e., the efficiency with oil is about 2 per 
cent, higher than with coal. 

As the other liquid fuels are largely used in internal-combustion en- 
gines no further discussion of them will be given at this point. 

Purchase of Fuel Oil under Specification, — The Bureau of Mines 
presents in Technical Paper No. 3 specifications for the purchase of fuel 
oil as applied by the Government. The essential features are: 

1. It should not have been distilled at a temperature high enough 
to burn it, nor at a temperature so high that flecks of carbonaceous matter 
began to separate. 

2. It should not flash below 60°C. (140°F.) in a closed Abel-Pensky or 
Pensky-Martens tester. 

3. Its specific gravity should range from 0.85 to 0.96 at 15°C. (59°F.) ; 
the oil should be rejected if its specific gravity is aboye 0.97 at that 
temperature. 

4. It should be mobile, free from solid or semisolid bodies, and should 
flow readily, at ordinary atmospheric temperatures and under a head of 
1 ft. of oil, through a 4-in. pipe 10 ft. in length. 

5. It should not congeal nor become too sluggish to flow at 0°C. 
(32°F.). 

6. It should have a calorific value of not less than 10,000 calories^ per 
gram (18,000 B.t.u. per pound) ; 10,250 calories to be the standard. A 
bonus is to be paid or a penalty deducted as the fuel oil delivered is above 
or below this standard. 

7. It should be rejected if it contains more than 2 per cent, water. 

8. It should be rejected if it contains more than 1 per cent, sulphur. 

9. It should not contain more than a trace of sand, clay or dirt. 
Causes for Rejection. — 1, A contract entered into under the terms of 

these specifications shall not be binding if, as the result of a practical 
service test of reasonable duration, the fuel oil fails to give satisfactory 
results. 

2. It is understood that the fuel oil delivered during the term of the 
contract shall be of the quality specified. The frequent or continued 
failure of the contractor to deliver oil of the specified quality will be con- 
sidered sufficient cause for the cancellation of the contract. 

Price and Payment. — 

1. Payment for dehveries will be made on the basis of the price named 
in the proposal for the fuel oil corrected for variations in heating value, 
as shown by analysis, above or below the standard fixed by the contractor. 
This correction is a pro rata one and the price is to be determined by the 
following formula: 

1 Calories X 1.8 = British thermal units per pound. 



FUELS 397 

Delivered calories per gram (or B.t.u. per pound) X contract price 
Standard calories per gram (or B.t.u. per pound) 

price to be paid. 

Water that accumulates in the receiving tank will be drawn off and 
measured periodically. Proper deduction will be made by subtracting 
the weight of the water from the weight of the oil deliveries. 

Gas. — Several different kinds of gas are commercially used as fuel. 
The most important are: 

(a) Natural gas. 

(6) Illuminating gas. 

(c) Coke-oven gas. 

{d) Producer gas. 

(e) Blast-furnace gas. 

The heating values of these different gases vary considerably under 
varying conditions — the first with different geographical locations; the 
others with variations in the fuels used and in details of operation in 
their manufacture. 

The following figures are fair average heating values for the gases 
under standard conditions (60°F. and 14.7 lb. per square inch). 

B.t.u. per cubic foot 
of standard gas 

Natural gas 1,000 

Illuminating gas 570 

Coke-oven gas 550 

{ Up-draf t plants 150 

Producer gas \ Double-zone plants 115 

[ Down-draft plants 110 

Blast-furnace gas ' 90 

Natural Gas under Steam Boilers. — Tests with natural gas under 
steam boilers indicate the consumption of "standard gas" per boiler 
horsepower to be from 38 to 60 cu. ft. in general although consumptions 
as high as 74 cu. ft. are reported. The corresponding efficiencies seem to 
range from 60 to 75 per cent, for normal commercial conditions with 
1,000-B.t.u. gas. At an efficiency of 74 per cent, the consumption would 
be apprr^ximately 45 cu. ft. per boiler horsepower. 

Absurd figures are sometimes reported which indicate test results as 
low as 17 or 18 cu. ft. of gas per boiler horsepower. 

In addition to the figures above, it may be well to point out that even 
with a gas of 1,100 B.t.u. per cubic foot and a furnace efficiency of 100 
per cent, the consumption must be 30.3 cu. ft. as shown below. 

One boiler horsepower = 970 X 34.5 = 33,400 B.t.u. which must be 
transmitted to the water. 

1,100 ~ '^^■'^- 



398 ENGINEERING OF POWER PLANTS 

Even with this high heat value gas and an efficiency of 75 per cent, the 
amount of gas required per boiler horsepower will be 

= 40.5 cu. ft. 



1,100 X 0.75 



J. M. Whitham {Transactions A.S.M.E., 1905) gives the following 
conclusions as a result of a series of investigations to determine the rela- 
tive value of blue flame and white flame gas under boilers: 

"1. There is but little advantage possessed by one burner over another. 

**2. As good economy is made with blue as with white or straw flame, and 
no better. 

"3. Greater capacity may be made with a straw- white flame than with a 
blue flame. 

"4. An efficiency as high as from 72 to 75 per cent, in the use of gas is 
seldom obtained under the most expert conditions. 

"5. The 'air for dilution^ is greater with gas than with coal, so possible coal 
efficiencies are impossible with gas. 

"6. Don't expect in good commercial practice to get a boiler horsepower on 
less than from 43 to 45 cu. ft. of natural gas (standard). 

"7. Fuel costs are the same under best conditions with natural gas at 10 cts. 
per 1,000 cu. ft. and semi-bituminous coal at $2.87 per 2,240 lb. (based on 3.5 
lb. of wet coal per boiler horsepower-hour or 45 cu. ft. of gas). 

"8. Expressed otherwise a long ton of semi-bituminous coal is equivalent to 
28,700 cu. ft. of natural gas. 

"9. As compared with hand-firing with coal in a plant of 1,500 boiler hp., coal 
being $2 per 2,240 lb., the labor saving by the use of gas is such that natural gas 
should sell for about 10 cts. per 1,000 cu. ft." 

It has been stated that the boiler horsepower handled by one fireman 
is seven or eight times as much with gas-fired boilers as with coal fired. 

Natural Gas for Domestic Heating. — As a result of investigations 
into the use of natural gas for domestic heating, W. F. M. Goss reached 
the following conclusions: 

1. In comparison with anthracite coal, gas is worth 6.8 cts. per 1,000 
cu. ft. for each $1 per ton charged for coal. 

2. In comparison with bituminous coal, gas is worth 8.1 cts. per 
1,000 cu. ft. for each Si per ton charged for coal. 

3. In comparison with first-class hickory wood, gas is worth 11.1 cts. 
per 1,000 cu. ft. for each Si per cord charged for wood. 

For example, taking values common in central Indiana, in comparison 
with anthracite coal at S7 per ton, gas is worth 47.6 cts. ; per 1,000 cu. ft., 
with bituminous coal at S3. 50, gas is worth 28.4 cts.; with hickory at $6 
per cord, gas is worth 66.6 cts. 



FUELS 399 

Advantages and Disadvantages of Various Fuels and of Electricity^ 



Fuel 


Advantages 


Disadvantages 


Wood 


(a) Cleanliness; (6) cheerful 


(a) Low fuel value; (6) large 




fire; (c) quick increase of 


storage space necessary; (c) 




heat; (d) cheap in some 


labor in preparation; {d) 




localities. 


scarcity; (e) does not hold 
fire long; (/) unsteady heat. 


Anthracite 


(a) Cleanliness; (6) easy con- 


(a) High price; (6) difficulty of 
obtaining; (c) slower response 




trol of fire; (c) easier to realize 




heat in coal than is the case 


to change of drafts. 




with other coals; {d) steady 






heat. 




Bituminous coal 


(a) Low price; (6) availability; 


(a) Dirty; (&) smoke produced; 




(c) high heat value (in the 


(c) more attention to fire and 




best grades) ; {d) low percent- 


furnace necessary than with 




age of inert ma.tter (in the 


anthracite. 




best grades). 




Sub-bituminous coal 


{a) Relatively low price; {h) 


(a) Slakes and deteriorates on 


and lignite: 


availability (in some regions) ; 


exposure to air; (&) takes fire 




(c) responds quickly to open- 


spontaneously in piles; (c) 




ing of drafts. 


heat value generally low; {d) 
heat in fuel difficult to realize; 
(e) fires do not keep well; (/) 
gases generated over fire pot 
sometimes burn in smoke 
pipe, causing excessive heat- 
ing. 


Peat 


(o) In general, the same as for 
wood. 


(a) Low heat value; (6) bulki- 
ness. 




Coke 


(a) Cleanliness; (6) responds 


(a) Bulkiness; (6) liability of 




quickly to opening of drafts; 


fire going out if not properly 




(c) fairly high heat value. 


handled; (c) fire requires 
rather frequent attention un- 
less fire pot is deep. 


Oil 


(a) High heat value; (6) imme- 
diate increase of heat; (c) 


(a) High price; (6) difficulty of 
safe storage. 






cleanliness; {d) small storage 






space necessary. 




Gas 


(o) Ease of control; (&) cleanli- 
ness; (c) convenience; {d) 
immediate increase of heat. 


(a) High price in many places. 


Electricity 


(a) Every advantage. 


(a) High price. 



1 Breckenridge. 



\ 



400 



ENGINEERING OF POWER PLANTS 
Cost of Energy in Fuels 



Kind of fuel 



Cost, $ 



B.t.u. as fired 



Number B.t.u. 
for $1 



Small anthracite . . 
Large anthracite . . 
Bituminous coal . . 
Bituminous coal. . 

Lignite 

Peat 

Fuel oil. 

Fuel oil 

Gasoline 

Gasoline 

Kerosene 

Kerosene 

Denatured alcohol 
Denatured alcohol 

Natural gas 

Natural gas 

Illuminating gas. . 

Coke-oven gas 

Producer gas 

Producer gas 

Producer gas 

Producer gas 

Blast-furnace gas . , 
Blast-furnace gas . , 



3 . 00 per ton 
7 . 00 per ton 
3.00 per ton 
1 . 50 per ton 
3 . 00 per ton 
3 . 00 per ton 

0.04 gaL 
0.02 gal. 
. 30 gal. 
. 10 gal. 
. 30 gal. 
. 10 gal. 
0.40 gaL 
. 30 gal. 



0.30 M 
0.10 M 
0.80 M 
0.80 M 
0.04 M 
0.02 M 
0.04 M 
0.02 M 
0.02 M 
0.01 M 



cu. ft. 
cu. ft. 
cu. ft. 
cu. ft. 
cu. ft. 
cu. ft. 
cu. ft. 
cu. ft. 
cu. ft. 
cu. ft. 



12,500 per lb. 
14,000 per lb. 
14,500 per lb. 
12,300 per lb. 

8,300 per lb. 

8,100 per lb. 



19,400 
19,400 
20,500 
20,500 
19,900 
19,900 
11,600 
11,600 

1,000 

1,000 

570 

550 

150 

150 

110 

110 

90 

90 



per lb. 
per lb. 
per lb. 
per lb. 
per lb. 
per Ibi. 
per lb. 
per lb. 

per cu. ft. 
per cu. ft. 
per cu. ft. 
per cu. ft. 
per cu. ft. 
per cu. ft. 
per cu. ft. 
per cu. ft. 
per cu. ft. 
per cu. ft. 



8,350,000 
4,000,000 
9,680,000 
16,440,000 
5,520,000 
5,400,000 

3,600,000 
7,300,000 

410,000 
1,230,000 

440,000 
1,320,000 

197,000 

263,000 

3,333,000 

10,000,000 

712,000 

689,000 

3,750,000 

7,500,000 

2,750,000 

5,550,000 

4,500,000 



PROBLEMS 

78. Check by Dulong's formula and by the approximate formula of page 376 the 
values of B.t.u. per pound for the fuels of page 405. 

79. Does the approximate formula of page 406 give a reasonable check for the 
B.t.u. value for Florida peat given on page 407? 

80. In response to a call for bids the following were received : 

A B CD E 

B.t.u (dry) 13,500 14,200 13,800 14,500 12,700 

Moisture, per cent 1.5 2.0 3.5 1.9 6.2 

Ash, per cent 8.0 9.2 7.5 5.2 8.5 

Volatile matter, per cent 29.5 28.0 26.5 21.0 30.4 

Sulphur, per cent 1.1 0.9 1.0 0.7 1.2 

Price per ton (2,000 lb.) $3.00 3.15 3.05 3.45 2.70 

Which bid offers the lowest cost per 1,000,000 B.t.u.? 

81. A coal contract specifies 13,500 B.t.u. (dry), 10 per cent, ash and 5 per cent, 
moisture at $2.50 per ton of 2,000 lb. delivered. The first lot of 1,000 tons averaged 
13,700 B.t.u. (dry) and 12 per cent, ash and 5.62 per cent, moisture. What should 
be the basis of payment per ton and what is the total bonus or forfeiture for the coal 
company on the 1,000 tons? 



FUELS 



401 



82. Two boilers, one fired with oil and one with the coal delivered in problem 66, 
each evaporate 180,000 lb. of water as metered during a 12-hr. run. The boiler 
efficiency was 72 per cent, with oil and 68 per cent, with coal. With oil at 3 cts. per 
gallon, what was the total cost of fuel for each of the 12-hr. runs? 
■ 83. A 500-hp. boiler is run 85 per cent, above rating. Determine : 

(a) The fuel cost for the plant for each of the fuels listed below for a period of one 
month of 30 days, 24 hr. per day, not including standby. 

(6) Determine the equivalent evaporation per pound of dry coal, per pound of 
oil, and per 1,000 cu. ft. of gas. 



Bituminous coal: 
Contract 

13,500 B.t.u. dry. 

6.5 per cent, moisture. 

8 per cent, ash in dry coal. 

$3.00 per ton (2,000 lb.). 
Oil: 

19,800 B.t.u. per pound. 
Natural gas : 

1,050 B.t.u. per cu. ft. 



Delivered 

14,000 B:t.u. dry. 

6.0 per cent, moisture. 

12.5 per cent, ash in dry coal. 



$0.90 per barrel (42 gal. 



$0.25 per 1,000. 



84. A 650-hp. boiler is run 200 per cent, above rating. Determine: 

(a) The fuel cost for the plant for each of the fuels listed below for a period of 6 

days, 24 hr. per day. 

(6) The equivalent evaporation per pound of dry coal, per pound of oil, and per 

1,000 cu. ft. of gas. 



Bituminous coal : 
Contract 

14,200 B.t.u. dry. 

4.5 per cent, moisture. 

7.5 per cent, ash in dry coal. 

$2.20 per gross ton. 
Oil: 

19,300 B.t.u. per pound. 
Natural gas : 

975 B.t.u. per cubic foot. 



Delivered 

13,900 B.t.u. dry. 

3.8 per cent, moisture. 

6.9 per cent, ash in dry coal. 



$1.00 per barrel (42 gal.). 



25 cts. per 1,000. 



85. (A) Determine the estimated fuel cost of evaporating in a steam boiler, 1,000 
lb. of water, under commercial operating conditions, with each of the following fuels: 
(a) Bituminous coal, 14,200 B.t.u. dry, 8 per cent, ash, 1.3 per cent, sul- 
phur, 7 per cent, moisture at $3.15 per ton of 2,240 lb. 
(6) Oil, 19,450 B.t.u. per pound at $1.20 per barrel of 42 gal., making 

allowance for the steam required for atomizer, 
(c) Natural gas, 990 B.t.u. per cubic foot at 25 cts. per 1,000 cu. ft. 
{B) With the least expensive fuel as a basis, determine the allowable cost of each 
of the other two fuels to make the fuel cost of evaporating 1,000 lb. of water the 
same for all three fuels. 

(C) Determine the equivalent evaporation: 
(a) Per pound of dry coal. 
(6) Per pound of oil. 
(c) Per 1,000 cu. ft. 



L 



CHAPTER XXI 
INTERNAL-COMBUSTION ENGINES 

In internal-combustion engines the pressure upon the piston is pro- 
duced by the expansion of a so-called '^explosive mixture." This explo- 
sive mixture consists of a combustible gas, vapor or oil mixed with air 
in such proportions that the mixture is easily ignited and upon ignition 
burns with such rapidity that a high temperature and high pressure are 
produced. The rate of burning is so rapid that it is commonly called an 
explosion. 

Four-cycle and Two-cycle Engines. — Two types of internal-combus- 
tion engines are commercially in use today, the four-cycle and the two- 



POWER- STROKE 1 




EXHAUST - STROKE 2L 





COMPRESSION - STROKE 4 





Fig. 219. 



cycle. In the four-cycle, or better four-stroke cycle gas engines, the 
events take place as indicated by the diagram, Fig. 219. 

Obviously there is, for a single-acting, single-cylinder engine but one 
power stroke for every two revolutions, and in commercial operation this 
power stroke may occasionally be missed, due to light load, improper gas 
mixture or failure of the ignition. 

This four-stroke cycle is frequently called the "Otto-cycle" in honor 
of the inventor of the engine, Dr. Otto. 

402 



INTERNAL-COMBUSTION ENGINES 



403 



In the two-cycle engine the suction stroke or pump stroke of the engine 
and the exhaust stroke are practically done away with. 

Two auxihary pumps are used for supplying to the engine cylinder 
gas and air at a pressure of about 10 lb. per square inch. The exhaust 
valves are annular openings in the cylinder wall near the end of the cylin- 
der and are uncovered by the piston as it nears the end of its stroke and 




70 



80 



90 



40 50 60 

% of Stroke 

Fig. 220. — Indicator card — two-cycle gas engine. 



100 



promptly covered by the piston as it reaches the same point on the return 
stroke. When the piston has completed about 0.9 of its stroke the ex- 
haust ports are uncovered, the burnt gases rush out and are followed by 
a rush of air from the air pump. 

This air tends to ''scavenge" the cylinder or free it from burnt gases. 
This air is immediately followed by gas in such proportions as to make an 





L J L 




[__ 


I r 1 J _ 1 


lJ 




> 








POWER Compression 
Exhaust POWER 
Suction Exhaust 

Compression Suction 



Suction Exhaust 

Compression Suction 
POWER Compression 
Exhaust 




POWER 

Fig. 221. — Sequence of events in the four-cycle double-acting system tandem 

cylinders. 

explosive mixture. This mixture is compressed upon the return stroke 
of the piston, ignited and expanded as in the four-stroke type. The ex- 
haust, scavenging and admission must take place in the time allowed for 
about 10 per cent, of one stroke. For an engine whose piston speed is 
750 ft. per minute this means that these operations must be accomplished 
in about 0.05 sec. This short time interval means high fluid friction losses. 



404 



ENGINEERING OF POWER PLANTS 



The irregularity of power impulses in the four-cycle engine may be 
readily overcome by placing two or more cylinders side by side and work- 
ing all on a single crankshaft, as is widely practiced with marine steam en- 
gines. Thus the three-cylinder engine gives a power impulse regularly at 
every two-thirds of a revolution, which has been found sufficient for very 
exacting work. Cranks are spaced 120° apart, or one-third of a circum- 
ference, so that power impulses occur at successive intervals of 240° 
rotation. 

The relative advantages and disadvantages of the two-cycle and four- 
cycle engines as pointed out by W. H. Adams^ for engines of the Diesel 
type practically hold good for all types of two- and four-cycle internal- 
combustion engines. Mr. Adams states that the two-cycle type gives 







TTl J 


- L 


i 


, 


, 


^ T 






lT 












- 




L J 






* . — ■* 




. 


r ' 




t 














' Y 





POWER Oompression 
POWER Oompression 

Exhaust POWER 

IMiaust POWER 

Suction Exhaust 
Suction Exhaust 

Oompression Suction 
Compression Suction 



Suction Exhaust 
Suction Exhaust 

Oompression Suction 
Oompression Suction 

POWER Compression 
POWER Compression 
Exhaust POWER 
Exhaust POWER 



'1st Stroke 
1st Stroke 
2nd Stroke 
2nd Stroke 

■ 3rd Stroke 
3rd Stroke 
4th Stroke 

! 4th Stroke 



Fig. 222. — Sequence of events four-cycle, double-acting twin tandem type. 



almost twice as much power for the same size of cylinder, as it has two 
working strokes for one in the four-cycle. (Actual value is 170 to 180 
per cent.) This means less weight, less space and less first cost. As 
usually constructed, the piston acts as its own valve and so air inlet and 
exhaust valves are not required. (This is not true of some of the better 
class of two-cycle Diesel engines, as will be explained later.) In marine 
work the reduction in number of valves makes it easier to reverse a two- 
cycle engine. The use of the two-cycle type has also made large units 
possible, and single-acting engines for 1,200 hp. per cylinder have been 
built. 

On the other hand, there is to be said for the four-cycle type of Diesel 
engine: 

1 "The Diesel Engine and Its Application in Southern California," by W. H. 
Adams, Transactions A.S.M.E. 



INTERNAL-COMBUSTION ENGINES 



405 



(a) It is older than the two-cycle type and so has become a more 
stable construction. 

(h) It gives better fuel economy, as expansion can be carried to the 
end of the stroke and no power is required for the scavenging pump. The 
gain is about 10 per cent. 

(c) The mean temperature is lower. There is more time to remove 
the heat and not so much heat to remove per unit of cylinder surface. 
(In a two-cycle engine 90,000 B.t.u. per hour have to be removed for every 
square foot of cylinder surface. In four-cycle engines the figure is 40,000 
B.t.u. In an ordinary water-tube boiler working at 300 per cent, of 
rating, it is 10,000 B.t.u.) 





M' ' '^M 




i 


Jgr-^i^lB 






^^K::^ ,,^^M 












» i^^^jEi^^B 


f 


'l9I h 


1 






^ 


»iilliWl|liSiiii^* 


i& 


'"" *'-:.:.'l ..,.•',.■"*, [ ■ Jj^'C/T-KV^^^ 


r. 




m^^^^^^^p -,^^'-'"7~^^B '' P-'^S'- 


' ""T"'''^^^^^ 


^^Bf 


! rj^jfe.;,,, 


mPMr^ 



Fig. 223. — Single-cylinder, single-acting, vertical gas engine. 

{d) The valve gear runs at one-half the speed of the main shaft. 

(e) In the high-speed two-cycle engine, it has been difficult to get the 
burnt gases out of the cylinder in the short time available, so that such 
engines have not been quite as successful as four-cycle engines. 

The tendency in this country and abroad is to use four-cycle engines 
up to from 700 to 1,000 hp. and above that two-cycle. This is due to the 
reduced first cost of the two-cycle type in the large sizes and the excessive 
diameter of cylinder required in large four-cycle engines. As progress 
is made in design, the two-cycle type may supersede the four-cycle, but 
this is not evident at present in the smaller sizes. 

26 



406 



ENGINEERING OF POWER PLANTS 



Horsepower. — The indicated horsepower of internal-combustion en- 
gines is found by the use of the same formula as for steam engines, viz : 



I.hp. = 



PLAN 
33,000 



in which 



P = m.e.p. in pounds per square inch. 
L = stroke in feet. 

A = effective piston area in square inches. 

N = number of times per minute the pressure is exerted on the 
piston. 

Although it is frequently convenient to determine the indicated horse- 
power of gas engines, and it is often desirable to do so, yet it should be 
remembered that although the indicated horsepower is generally used in 




Fig. 224. — Single-cylinder, single-acting horizontal gas engine 



purchasing steam engines, the brake, or effective, horsepower is used in 
contracts of sale of gas engines. 

In computing the brake horsepower from the cylinder dimensions and 
speed of four-cycle engines it is customary to assume mean effective pres- 
sures of 66, 68 or 70 lb. per square inch and a mechanical efficiency of 
85 per cent. 

An idea of the relation between cylinder dimensions and horsepower 
for two-cylinder, tandem, double-acting, four-cycle engines may be had 
from the following table: 



INTERNAL-COMBUSTION ENGINES 



407 



Diam. cyl., in 

Stroke cyl., in 

Rev. per min 

Piston speed, ft. per 

min 

Rated b.hp — 

Factor C. 

Diam. cyl., in 

Stroke, in 

Rev. per min 

Piston speed, ft. per 

min 

Rated b.hp 

Factor C 



18 

24 

150 

600 
260 
0.8 

34 

42 
100 

700 
1,105 
0.96 



20 

2A 

150 

600 
320 
0.8 

36 

48 
92 

736 
1,300 
1.00 



21 

30 

125 

625 

370 

0.84 

38 
48 
92 

736 
1,460 
1.01 



22 

30 

125 

625 

405 

0.84 

40 
48 
92 

736 
1,630 
1.02 



24 

30 

125 

625 

490 

0.85 

42 
54 



774 
1,875 
1.06 



24 

36 

115 

690 

545 

0.95 

44 
54 
86 

774 
2,080 
1.07 



26 

36 

115 

690 

630 

0.93 

46 
54 
86 

774 

2,280 

1.08 



28 

36 

115 

690 

740 

0.94 

48 
60 

78 

780 

2,475 

1.07 



30 

42 

100 

700 

855 

0.95 

50 
60 

78 

780 

2,720 

1.09 



32 

42 

100 

700 

985 

0.96 

52 
62 

78 

780 
2,950 
1.09 



For determining the approximate horsepower of small automobile- 
type gasoline engines, the A.L.A.M. has adopted a formula 



b.hp. = 



diam. 2 X no. cylinders 
2l 



This assumes a piston speed of 1,000 ft. per minute. On this basis the 
following ratings are derived, as given by Kent (page 1101, 9th edition) : 



Bore, in 

Bore, mm 

Hp., 1 cylinder. 
Hp., 2 cylinders 
Hp., 4 cylinders 
Hp., 6 cylinders 



2.5 

64.0 

2.5 

5.0 

10.0 

15.0 



3.0 

76.0 

3.6 

7.2 

14.4 

21.6 



3.5 

89.0 

4.9 

9.8 

19.6 

29.4 



4.0 
102.0 

6.4 
12.8 
25.6 
38.4 



4.5 
114.0 

8.1 
16.2 
32.4 
48.6 



5.0 
127.0 
10.0 
20.0 
40.0 
60.0 



5.5 

140.0 

12.1 

24.2 
48.4 
72.6 



6.0 

154.0 

14.4 

28.8 
57.6 
86.4 



For two-cycle engines of the power-boat type the American Power 
Boat Association uses: 

b.hp. = area of piston X no. cylinders X length of stroke X 1.5 

It should be remembered that the rating of gas engines is such, due 
to increased economy with increase of load, that they cannot respond to 
heavy overload demands. 

In order that the purchaser may have a definite idea of what he is 
buying and feel sure of an * 'overload leeway," the prevailing practice 
seems to be so to rate gas engines that they will respond to and maintain 
a load 20 per cent, above that specified in the contract as the normal 
rating of the engine. 

It must not be forgotten that the power of a gas engine varies with 
the atmospheric pressure and consequently with change in elevation. 



408 ENGINEERING OF POWER PLANTS 

li p = barometric pressure at sea level, 
Pe = barometric pressure at elevation, 
hp. = horsepower at sea level, 
hp.c = horsepower at elevation, 
then 

hp.e = — ^hp. 
p 




Fig. 225. — Section of single-acting, four-cycle vertical gas engine. 

Piston Speeds. — Gas-engine piston speeds run approximately as fol- 
lows: 

Small stationary engines, 400 to 600 ft. per minute. 
Large stationary engines, 500 to 1,000 ft. per minute. 
Automobile engines, 600 to 1,000 ft. per minute. 

Regulating or Governing. — ^Levin states^ that the factors that deter- 
mine the output of an engine are: The amount of gas admitted, the 

1 "Modern Gas Engine and the Gas Producer," by A. M. Levin, John Wiley 
and Sons. 



INTERN AL'COMBUSTION ENGINES 



409 



amount of air admitted, the compression effected, and the timing of the 
ignition. 

To effect governing, two or more of these features are generally- 
changed simultaneously. 

In the hit-or-miss system the gas alone, or the gas and air, are shut 
off entirely at excessive speeds, but other features remain unchanged. 

In throttling an already completed mixture the gas and air volumes 
are changed proportionally, and, thus, the quality of the charge remains 
unchanged, but the compression will be diminished. 




Fig. 226. — Three-cylinder, four-cycle, single-acting vertical gas engine. 

By having the gas and air throttle controlled separately, the quality 
of the mixture may be changed, but the quantity unchanged, and thus 
the compression unchanged. 

Between these proportions the quality of the charge may be changed 
to any extent, resulting in a more or less decreased compression. It may 
even be possible to dilute the charge to such an extent that its quantity 
and compression become greater at reduced loads. 

Mechanical Efficiency of Gas Engines. — Tests of both four- and two- 
cycle engines show the following relative mechanical efficiencies: 



Four-cycle 

74 to 92 
Avg. = 85 



Two-cycle 

63 to 75 
Avg. = 70. 



410 



ENGINEERING OF POWER PLANTS 



Owing to the difficulty often encountered in obtaining the indicated 
horsepower of gas engines under operating conditions, and owing to the 




lack of rehability in determining the indicated horsepower from indicator 
cards save by experienced men, it is advisable to determine the friction 



INTERNAL-COMBUSTION ENGINES 



411 



horsepower of a gas engine by careful tests and thereafter use this value 
in determining the mechanical efficiency of the engine, as many investi- 
gations have shown the friction horsepower of such engines to be suffi- 
ciently constant to warrant this procedure. 

For example, take the tests on gasoline and alcohol engines reported 
in U. S. Bureau of Mines, Bulletin No. 43. 



Brake 
horsepower 



Indicated 
horsepower 



Friction 
horsepower 



Per cent, 
rated load 



Mechanical efficiency 



b.hp. 
i.hp. 



X 100 



b.hp. 



b.hp. + avg. f.hp. 



X 100 



Otto 15-hp. gasoline engine 



17.16 


19.34 


2.18 


114.3 


88.8 


88.3 


15.98 


18.30 


2.37 


106.7 


87.3 


87.6 


- 15 . 40 


17.70 


2.30 


102.8 


87.0 


87.1 


14.80 


16.90 


2.10 


98.6 


87.5 


86.7 


14.18 


16.22 


2.04 


94.5 


87.4 


86.2 


13.66 


15.87 


2.21 


91.0 


86.1 


85.8 


12.41 


14.70 


2.29 


82.9 


84.4 


84.6 


9.98 


12.29 


2.31 


66.5 


81.4 


81.5 


7.60 


10.18 


2.58 


50.7 


75.3 


77.0 


5.09 


7.49 


2.40 


34.0 


68.0 


69.2 


Avg. frictional horse- 














power for 245 tests .... 


2.27 









Nash 10-hp. gasoline engine 



15.10 


17.74 


2.64 


151.0 


85.2 


86.4 


13.78 


15.75 


1.97 


137.8 


87.5 


85.2 


14.00 


15.04 


1.04 


140.0 


91.6 


85.4 


12.80 


16.11 


3.31 


128.0 


79.5 


84.3 


11.73 


13.89 


2.16 


117.3 


84.5 


83.1 


11.28 


13.82 


2.54 


112.8 


81.6 


82.6 


10.76 


12.58 


1.82 


107.6 


85.6 


81.9 


10.51 


13.19 


2.68 


105.1 


79.6 


81.5 


10.17 


12.14 


1.97 


101.7 


83.8 


81.0 


9.36 


12.05 


2.69 


93.6 


77.8 


79.7 


8.22 


10.78 


2.56 


82.2 


76.3 


77.5 


7.99 


9.87 


1.88 


79.9 


81.0 


77.0 


7.08 


9.55 


2.47 


70.8 


74.5 


74.8 


, 6.06 


8.20 


2.14 


60.6 


73.9 


71.7 


4.72 


7.25 


2.53 


47.2 


65.9 


66.4 


Avg. frictional horse- 










power for 104 tests .... 


2.39 









412 



ENGINEERING OF POWER PLANTS 



The figures above represent test conditions. The following data from 
engines operating under rather harsh conditions are, therefore, of com- 
parative interest. These tests on pumping engines in operation in Cali- 
fornia were made under the direction of the Government. 

They show that the power consumed in friction is approximately 
constant for a given speed, without regard to the useful work done. They 
also show the uneconomical results that come from using an engine too 
large for the work. 



Brake 
horsepower 



Indicated 
horsepower 



Friction 
horsepower 



Per cent, 
lated load 



Mechanical efficiency 



b.hp. 
i.hp. 



X 100 



^ • ^-^P- ,^ X 100 
b.hp. + avg. f .hp. 



Fairbanks-Morse .25-hp. gasoline engine 



9.3 


16.9 


7.6 


37.2 


55.0 


56.4 


8.0 


15.2 


7.2 


32.0 


52.6 


52.6 


6.7 


13.4 


6.7 


26.8 


50.0 


48.2 


5.4 


12.6 


7.2 


21.6 


42.8 


42.8 


4.0 


11.6 


7.6 


16.0 


34.5 


35.7 


0.0 


6.7 


6.7 


0.0 


0.0 


00.0 


Avg 




7.2 

















White and Middle ton 30-lip. gasoline engine 




11.8 


18.5 


6.7 


39.0 


64.0 


64.0 


8.0 


16.0 


.7.1 


26.7 


50.0 


54.4 


5.9 


11.7 


5.8 


19.7 


50.4 


46.8 


2.9 


10.1 


7.2 


9.7 


28.7 


30.2 


Ave 




6.7 















Thermal Efficiency and Economy. — If there are no losses, 1 B.t.u. 
per minute would give 778 ft.-lb. per minute behind the piston, 60 
B.t.u. per hour would give the same. 

T>4. -v. 1. 33,000 X 60 ^.,. ;. 1 . 1. . 

B.t.u. per i.hp.-hr. = ^^ = 2,545 with no losses of any kind 

Thermal efficiency = B.t.u. p^ min.Sfuel X 778' 

Thermal efficiency = 3^^ per min.Sfuel X 778' 
Although very wild claims are made by some manufacturers regarding 
the thermal efficiencies of their engines, it is probable that the maximum 
thermal efficiency of such engines under the most favorable operating 



INTERNAL-COMBUSTION ENGINES 



413 




414 



ENGINEERING OF POWER PLANTS 



conditions^ is about 38 per cent., based on the indicated horsepower, or 
30 per cent, based on the brake horsepower. 

One engine is reported to have developed a brake horsepower-hour on 
7,200 B.t.u. but this is very exceptional. Under working conditions gas 
engines are expected to produce a brake horsepower on from 9,000 to 




Fig. 229. — Horizontal, twin-tandem, double-acting four-cycle gas engine. 

12,000 B.t.u. per hour. The average of several quotations from different 
manufacturers is as follows: 



Per cent, rated load 100 75 

B.t.u. per b.hp.-hr. 10,500 12,000 



50 
14,700 



25 
20,000 



One reliable firm guarantees under operating conditions for the same 
per cent, of load 10,500, 11,500, 14,000, 20,000 B.t.u. per hour. 

These guarantees will, of course, vary somewhat with the gas used, 
but the average values will give a fair basis for estimates. 

Comparative Results from Denatured Alcohol and Gasoline. — The 
possibilities from denatured alcohol in internal combustion engines are 
so good that a brief summary of the important results from 2,000 tests 
with gasoline and alcohol at the United States Bureau of Mines Testing 
Station is presented: 



1 The theoretically possible thermal efficiency of the Otto engine is 52 per cent, 
and of the Diesel 57 per cent. 



INTERN AL'COMBVSTION ENGINES 415 

Gasoline Alcohol 

Hp. of engines 10 and 15 10 and 15 

Best compression pressure, lb., sq. in • 70 180 

Maximum explosion pressure, lb., sq. in. . . . .... 600 to 700 

Fuelperb.hp.-hr., lb... 0.60 0.71 

Fuel per b.hp.-hr., gal 0.10 0.10 

General Conclusions. — 

(a) For engines of the same cylinder size, but with 70 lb. compression 
for gasoline and 180 lb. for alcohol, the maximum available horsepower 
of the alcohol engine is about 30 per cent, greater. 




Fig. 230. — 500-hp. vertical marine gas engine. 

(b) With the compression pressures indicated, the engines required 
equal volumes of gasoline and denatured alcohol, respectively, per horse- 
power-hour, namely, about 1 pt. 

(c) If alcohol be used in an engine with a compression designed for 
gasoline, the engine will require about 50 per cent, more alcohol than gaso- 
line per horsepower-hour. 

(d) Alcohol diluted with water in any proportion up to about 50 per 
cent, can be used in gasoline or alcohol engines if the engines are properly 
adjusted. 

Pressures and Temperatures. — The degree of compression possible 
with explosive mixtures used in internal combustion engines varies with 
the fuel used. Under normal conditions with engines working on the 
OttQ cycle the allowable compression pressure will be approximately: 



416 ENGINEERING OF POWER PLANTS 

Fuel Pounds per 

square inch 

Kerosene 50 to 75 

Gasoline 70 to 90 

Alcohol 70 to 200 

Illuminating gas 70 to 90 

Natural gas 90 to 140 

Producer gas 120 to 200 

Blast-furnace gas 130 to 200 

After combustion the pressure is much higher, usually running from 
250 to 400 lb. per square inch and not infrequently reaching 600 or 700 
lb. per square inch. 

The temperature after combustion usually reaches 2,200°F. to 2,500°F. 
and may at times reach 3,000°F. 

In the Diesel engine the initial compression reaches 500 to 550 lb. 
per square inch and the compression temperature is in the neighborhood 
of 1,000°F. 

The two great sources of heat loss in internal combustion engines are 
due to the high temperature of the exhaust gases and the heat trans- 
ferred through the cylinder walls to the jacket water. 

The temperature of the gases at release is often from 1,500 to 1,800°F. 

Circulating Water. — To remove the excess heat from the cyUnder walls 
and in large engines from the pistons, piston rods and exhaust valves, 
water is circulated through cored passageways. 

The amount of cooling water required per horsepower-hour is stated 
by different investigators as: 

T i- J. „ Cubic feet per 

Investigator horsepower-hour 

a 0.67 to 0.93 

b 0.83 to 1.03 

c 0.40 to 0.80 

d 0.73 to 0.73 

e 1.20 to 1.47 

/ 0.67 to 1.07 

Average 0.75 to 1.00 

The U. S. Bureau of Mines figures average for a large number of tests 
0.82 cu, ft. per horsepower-hour for a three-cylinder, single-acting engine 
of 250-hp. rating. 

The wide variation in practice in commercial plants may be seen by 
comparing the following figures covering long-time periods for plants in 
daily operation. 

The high average is undoubtedly due in part to the fact that water 
cost little or nothing at most of these plants. 

The initial temperatures reported for the cooling water for these 



INTERNAL-COMBUSTION ENGINES 417 

Cubic feet per 
Plant horsepower-hour 

1 3.36 

2 2.80 

3 2.56 

4 1.01 

5 2.18 

6 2.56 

Average 2.41 

installations range from 50° to 90°F. and the outlet temperatures from 
86° to 160°F., the average being 115°F. 

In general there may be said to be at present a tendency toward higher 
temperatures of circulating water than in the past. Until within a few 
years 160° was regarded as about the upper commercial limit but recent 
practice in special plants has been to put the jacket water under pressure 
and to increase its temperature to about 300°F. or more. 

For small engines it may pay to install tanks or reservoirs for the cir- 
culating water. If this is done and the circulation is maintained by the 
difference in the specific gravity of the hot and cold water, the size of the 
tanks should be sufficiently large to enable the engine to run smoothly 
at maximum load for several hours consecutively. The reservoirs should 
then have a capacity of 50 to 65 gal. per horsepower hour. 

For large installations when water is expensive, cooling towers 
are often installed or spray ponds built as in condensing steam-engine 
practice. 

Lubrication. — Owing to the high temperatures that prevail in the 
cylinder of the internal-combustion engine, the question of proper 
lubrication is a serious one. Cylinder oil should be exceedingly pure, free 
from acids, and composed of hydrocarbons that leave no residue after 
combustion. Only mineral oils, therefore, are suitable for the purpose. 
The ignition point of good cylinder oil should not be lower than 535°F. 
The losses in power due to poor lubrication of gas engines may amount 
to 10 or 15 per cent. 

The amount of oil required per horsepower-hour varies with the char- 
acter of the installation and the method of operation. For full-load 
24-hr. service, the proportion per horsepower-hour is, of course, 
greater than for a plant running under light load for a 9- or 10-hr. day. 

The average of several figures given by the engine manufacturers for 
the amount of engine oil required is 0.508 gal. per 1,000 hp.-hr. 

The operators of plants, however, report their commercial require- 
ments to be : 



418 



ENGINEERING OF POWER PLANTS 
Gallons per 1,000 Hp.-Hr. 



Horsepower of 
engines 


Hours of service 
per das'- 


Cylinder oil 


Engine oil 


Other 
lubricants 


100 


8 


2.0 






100 




1.8 


1.3 


1.25 


40, 160 


16 


2.8 






190 


24 





1.0 




500 


24 


1.25 






80, 160, 200, 375 


12 


1.5 


3.0 




200, 500 


24 


.... 


1.26 




300 


24 


0.75 


0.4 


0.8 


750 


10 


0.5 


0.17 


0.07 


125 




0.13 


0.4 


0.1 


150, 250, 300, 600 




0.5 


1.0 




500 


10 


0.5 


0.6 


0.14 


500, 1,000 


10 


0.4 


0.6 




300, 2,000 


24 


2.7 


5.3 


0.7 


115, 300, 750 


24 


0.25 


0.5 






24 


1.25 










Average 


•• 


1.17 


1.11 


51 







The average of a number of returns from the operators of reciprocating 
steam engines indicates the consumption of cyhnder oil and engine oil 
to be approximately the same and to equal 0.13 gal. each per 1,000 hp,-hr. 
On this basis the oil consumption of gas engines seems to be approximately 
eight or nine times as much as that of reciprocating steam engines. This 
is perhaps not unreasonable as the lubricating requirements of the gas 
engine are much more severe than those of the steam engine, but the 
ratio seems rather high. 

Advantages of the Intemal-combustion Principle. — 

1. The energy of the heat liberated by combustion operates directly 
upon the piston of the engine to produce motion, without intervening 
appliances. 

2. The economy in fuel per horsepower is greater than with steam. No 
fuel consumed wastefully in getting the motor ready to start. In plants, 
other than producer-gas plants, more nearly portable than steam plants. 

3. Insurance lowered by absence of boiler under pressure but some- 
times offset by gas-holder, or stored liquid fuel. 

4. Absence of boiler avoids necessity of licensed operators. 

5. Motor ready to start without previous preparation except with 
gas producer. 

6. When fuel cut off, engine stops, not always a gain with gas producer. 

7. Advantage of subdivided power, as each motor may receive its 
gas without loss through pipes, or from fuel tanks. 



INTERNAL-COMBUSTION ENGINES 419 

8. No storage of large amounts of energy under pressure, in a contain- 
ing vessel, the rupture of which will cause disaster. 

9. No boiler to cause trouble from bad water. 

10. Normal and proper combustion smokeless. 

11. Reduction in dust, sparks, ashes, etc., even with producers. 
Disadvantages. — 

1. In Otto cycle only one stroke in four is power stroke. In two-cycle 
only one in two. On this account for a given mean pressure a large 
cylinder volume is required, especially for single-acting engines. 

2. Irregular crank effort. Heavy flywheel needed. If a number of 
cylinders are used the engine itself becomes heavy. 

3. Motor does not start from rest by a simple motion of a lever or 
valve. This involves a clutch. 

4. No way of increasing the power beyond the limit set by the diame- 
ter of the cylinder. 

5. No storage of energy for overload demands, etc., as in the boiler, 
save in the producer system. 

6. Have to cool cylinder and other parts of the engine with water. 

7. Large amount of heat carried away, unutilized, by the jacket water. 

8. In spite of cooling water, the valves become leaky and require 
attention. 

9. If not carefully looked after in making the installation, the ex- 
haust is noisy. 

10. High temperature makes lubrication difficult. 

11. If combustion not complete odor of exhaust offensive. 

12. May get explosions in exhaust pipes or reservoirs. 

13. Governing difficult on variable loads. 

14. Not usually reversing in action. 

15. Efficiency a maximum only near full load and when up to speed. 
Rapid Development of the Gas Engine. — It was during the latter 

part of the nineteenth century that the gas engine found its way on to 
the market, and, although many types have been produced in the past 
30 or 40 years, it is only within the past 10 or 15 years that the devel 
-opment of large engines has been noted. This development started in 
England, Belgium and Germany but marked progress has been limited 
to the past dozen years. 

For many years the natural fuel of these internal-combustion engines 
was city gas, but even this was too expensive except for engines of small 
capacity. It was seldom found feasible to operate engines of more than 
75 hp. on this fuel. 

Cheap gas was essential for the development of the gas engine, but 
early attempts in this direction were somewhat discouraging, and for a 



420 ENGINEERING OF POWER PLANTS 

time the probabilities of encroaching to any extent upon the field occu- 
pied by the steam engine were very remote. 

The theoretical possibilities of the internal-combustion engine oper- 
ated upon cheap fuel promised so much that the practical difficulties 
were rapidly overcome with the result that steam boilers and engines in 
many plants were replaced by gas engines, and at the present time the 
internal-combustion engine is a serious rival of the steam engine in many 
of its apph cations. 

The development of the gas engine in point of size has been exceedingly 
rapid. It was in 1900 that a 600-hp. engine exhibited at the Paris Ex- 
position was regarded as a wonder, but today four-cycle, twin-tandem, 
double-acting engines of -2,000 to 3,500 hp. can be found in nearly all 
up-to-date steel plants, and there are installations in this country con- 
taining several units rated at 5,400 hp. each. 

Marine engines of the Diesel type have reached 1,200 hp. per cylinder, 
or 7,000 hp. in six cylinders, all single-acting. 

Proper Location for a Gas Engine. — A gas engine should be located 
in a well-lighted place, accessible for inspection and maintenance and 
should be kept entirely free from dust. As a general rule the engine 
space should be enclosed. An engine should not be located in a cellar, 
on a damp floor, or in badly illuminated and ventilated places. 

The pipes by which fuel is conducted to engines, the gas bags, etc., 
are rarely altogether free from leakage, especially if the fuel used be street 
gas, or natural gas. For this reason the engine room should be as well 
ventilated as possible in the interest of safety. Long lines of pipe 
between the meter and the engine should be avoided, for the sake of 
economy, since the chance for leakage increases with the length of pipe. 
Not infrequently the leakage of a pipe 30 to 50 ft. long, supplying a 
30-hp. engine, may be as much as 90 cu. ft. per hour. 

An engine should be supplied with gas as' cool as possible, which con- 
dition is seldom realized if long pipe lines be employed for city or natural 
gas, extending through workshops, the temperature of which is usually 
higher than that of the underground piping. On the other hand, pipes 
should not be exposed to the freezing temperature of winter, since the 
frost formed within the pipe, and particularly the crystalline deposits of 
naphthaline, reduces the cross-section and sometimes clogs the passage. 
Often it happens that water condenses in the pipes; consequently, the 
piping should be so arranged as to avoid pockets. In places where water 
can colect, a drain pocket or plug should be provided so that liquid can 
be introduced to dissolve the naphthaline. 

Starting Gas Engines. — Various methods have been used for starting 
these engines. Among the most common are : 

1. Hand-starting with flywheel or independent crank. 



INTERNAL-COMBUSTION ENGINES 421 

2. In multi-cylinder engines, by hand pumps. 

3. Compressed air [most usual today]. 

4. Storage of compressed explosive mixture. 

5. Independent engine for starting in large plants. 

6. Various explosives. 

Exhaust Pipe.— If the exhaust pipe must be long, the use of elbows 
or sharp bends should be avoided as far as possible. In the case of very 
long pipes it is advisable to increase their diameter every 16 ft. from the 
exhaust. 

For the sake of safety, at least that portion of the piping which is near 
the engine should be located at a proper distance from woodwork and 
other combustible material. Great care must be taken if the exhaust 
be discharged into a sewer or chimney, even though the sewer or chimney 
be not in use; for the unburnt gases may be trapped, and dangerous ex- 
plosions may ensue at the moment of discharge. 

When several engines are installed near each other, each should be 
provided with a special exhaust pipe, especially if the engines are to be 
in operation at the same time; otherwise the exhaust of one may cause 
excessive back-pressure on the others. 

Exhaust Noises. — Among the most difficult noises to muffle is that 
of the exhaust. The most commonly employed means is to extend the 
exhaust pipe upward as far as possible, even well above the roof. This 
reduces the noise to some extent, but is not very efficient and produces 
back-pressure on the engine. Exhaust mufflers help to some extent, and 
the employment of pipes of sufficiently large cross-section to constitute 
expansion boxes in themselves will also muffle the exhaust. Consider- 
able benefit has been derived from specially designed exhaust pipes, con- 
structed on such lines that the gases have an opportunity for rapid ex- 
pansion immediately after leaving the engine. This condition is secured 
by a gradual expansion of the pipe for a distance of a few feet from the 
engine. 

A more complete solution of the problem is obtained by causing the 
exhaust pipe after leaving the muffler to discharge into a masonry trough 
having a volume equal to 12 times that of the engine cylinder. One 
authority states that the trough should be divided into two parts, sepa- 
rated by a horizontal iron grating. Into the lower part, which is empty, 
the exhaust pipe discharges; in the upper part paving blocks or hard 
stones not likely to crumble with the heat are placed. Between this layer 
of stones and the cover it is advisable to leave considerable space. Here 
the gases expand after having been divided into many parts in passing 
through the spaces left between adjacent stones. The trough should not 
be closed by a rigid cover; for although efficient muffling may be attained, 
yet an explosive mixture may be formed in the trough and damage caused. 

27 



422 



ENGINEERING OF POWER PLANTS 



The explosion is, however, less dangerous than noisy. Some authorities 
claim the only use of stones in the pit is to prevent the possibility of 
accident to careless people. 

Weight of Gas Engines. — It is interesting to note the wide variation 
in weights per horsepower of different types of gas engines. 



Type 



Weight per 

horsepower, 

pounds 



Aero 2 . 5 to 4 

Motor boat 35 to 40 

City gas, natural gas or gas- 
oline 200 to 250 

Oil 250 to 500 

Producer gas or bla,st-fumace 

gas « . . 200 to 600 Avg. 300 in Europe. 

400 in United States. 

COST OF GAS ENGINES 

Cost of Gas Engines for City or Natural Gas 



Horsepower 


Engine, f.o.b., 
dollars 


Cost per horse- 
power, f.o.b., 
dollars 


Horsepower 


Engine, f.o.b., 
dollars 


Cost per horse- 
power, f.o.b., 
dollars 


20 


700 


35.00 


100 


3,550 


35.50 


20 


860 


43.00 


100 


3,830 


38.30 


22 


775 


35.20 


125 


4,100 


32.80 


25 


875 


35.00 


125 


4,475 


35.80 


27 


1,25« 


46.30 


135 


4,200 


31.10 


30 


1,130 


37.70 


140 


6,980 


49.90 


35 


1,600 


45.75 


150 


4,856 


32.40 


50 


1,650 


33.00 


160 


5,230 


32.70 


50 


1,800 


36.00 


175 


5,750 


32.80 


50 


1,960 


39.20 


175 


6,275 


35.80 


50 


2,000 


40.00 


195 


7,300 


37.40 


100 


3,400 


34.00 


200 


5,600 


28.00 








360 


13,400 


37.25 





Cost of Kerosene Engines 






Horsepower 


Engine, f.o.b., 
dollars 


Cost per horse- 
power, f.o.b., 
dollars 


Horsepower 


Engine, f.o.b., 
dollars 


Cost per horse- 
power, f.o.b., 
dollars 


1 

2 
4 
6 

8 


121 
204 
324 

444 

568 


121.00 

102.00 

81.00 

74.00 

71.00 


10 
15 
20 
30 
40 
60 


650 
855 
1,060 
1,450 
2,020 
2,820 


65.00 
57.00 
53.00 
48.40 
50.50 
47.00 



INTERNAL-COMBUSTION ENGINES 



423 



Cost op Producer Gas Engines 



Horsepower 



Cost, 

f.o.b. 

factory- 



Cost 

of 

erecting 



Founda- 
tion, 
cubic feet 



Cost of 
founda- 
tion 



Cost of 

engine 

erected 

including 

foundation 



Cost per horsepower 



F.o.b. 
factory- 



Erected, 
including 
founda- 
tion 



20 
55 
60 
60 

^75- 

80 
80 
80 
80 
85 

85 
100 
110 
110 
112 

130 
135 
160 
160 
250 

400 

400 

600 

1,000 

2,000 



1,000 

2,800 
2,900 
3,610 



3,400 
3,250 
3,830 
4,150 

3,550 
4,925 
4,950 
4,960 
4,200 

5,250 
6,600 
5,500 
6,100 
6,650 

12,000 
12,800 
17,400 
33,750 
64,850 



175 



350 
375 



150 
100 



300 

875 



2,000 
2,160 



5,400 



50 



105 
150 
150 



225 



520 
560 



1,400 



1,150 
2,400 



3,935 
3,300 



6,770 
7,360 



67,125 



55.00 

46.70 
48.40 
48.10 



42.50 
40.70 
40.90 
48.90 

41.80 
49.25 
45.00 
45.10 
37.50 

40.40 
48.80 
35.00 
38.10 
26.60 

30.00 
32.00 
29.00 
33.75 
32.43 



43.70 



52.40 



41.20 



42.30 
29.40 



33.56 



The Oil Engine.— 

As early as 1873 Brayton tried kerosene oil in a two-cycle engine, 
burning the fuel directly in the cyhnder at constant pressure. Theoretic- 
ally this should have given an efficiency of more than 50 per cent. 

Unfortunately, the losses attendant on the compression of the air and 
the fuel, with the difficulties of finding a burner and controlling the con- 
stant-pressure flame became so serious that the manufacture of the engine 
was discontinued. 

The first attempt to develop an oil engine on the Otto cycle was prob- 
ably that of Priestman, who in 1888 succeeded in constructing an engine 
which worked on heavy petroleum distillate in a very satisfactory man- 



424 



ENGINEERING OF POWER PLANTS 



ner. 



Priestman used an ordinary four-cycle Otto engine, but injected 
his oil into a vaporizer by means of the reflex rose spray nozzle, the oil 
dropping into the center of the spray by gravity and the small pump 




Fig. 231.— DeLaVergne type F. oil engine. 

compressing the air for use in this apparatus. The spray was received 
in a cast-iron outside-heated vaporizer and the ordinary Otto cycle was 
carried on with this gas in the customary manner. 




Fig. 232.— Nordberg heavy oil engine. 



Most of the engines built in England from that time to this have been 
more or less on the Priestman principle, although the Hornsby Akroid 
which come out in 1892 uses an externally heated extension of the cylinder 



INTERNAL-COMBUSTION ENGINES 



425 



compression space as a vaporizer, the oil being forced into this chamber 
by means of a small pump and as the piston returns on the compression 
stroke the heating of the charge of air reaches a point at which the density 
of the mixture is such that it will ignite directly from the hot chamber. 
In the Brayton engine flame ignition was necessary. In the Priestman 
engine electrical ignition was used and with the Hornsby Akroid what 
amounts to hot-tube ignition is the standard. Many varieties of these 
engines are in use today. In niany of these engines there is sufficient 
heat developed in the compression space to ignite the charge, in others 
the hot-tube ignition must be used. Among the successful engines of 
this type are the DeLaVergne, the Mietz and Weiss and many others. 




Fig. 233. — Horizontal Diesel engine, 30 b.hp. 



It is to be noted that most of these modern oil engines employ com- 
paratively low compression. One hundred and fifth pounds is high, from 
80 to 100 is perhaps higher than the average. Some trouble results from 
the carbonization of the fuel in the compression space from imperfect 
burning and from the gumming up of the small oil passages. In most of 
these engines the cylinder heads and the vaporizing hot tubes must be 
cleaned once or twice in 24 hr. if economical running is at all a necessity. 

There is another type of engine in which an auxiliary compression 
cylinder in the cylinder head is used to compress a small portion of the 
mixture up to the ignition point. A number of small engines have been 
built on this principle. 



426 ENGINEERING OF POWER PLANTS 

There are three methods of securing the vaporized mixture. The 
first is the spray and outside-heated hot vaporizer, in which a very rich 
mixture of atomized oil and air is heated in a cast-iron receptacle. The 
entrance into the hot tube is constricted and the air admission is by a 
separate valve into the cylinder itself. The compression of the air on 
the return stroke of the piston forces a sufficient volume of air into the 
hot tube to get the required mixture for explosion. The second is the 
comparatively large vaporizer with many baffles which is heated by 
the exhaust gases of the engine. Into this vaporizer the oil is fed drop by 
drop, falling on the hot surfaces where it is vaporized. This chamber is in 
communication with an inlet valve and the air passes through the vapor- 
izer making a proper mixture for explosion. The first plan is self-igniting, 
the second plan requires an electrical igniter. 

The third system is a modification of the second in which the air 
supply is partly used in atomizing the fuel and is partly taken in in the 
ordinary way. This also requires electric ignition. 




Fig. 234. — Indicator card of Diesel engine. 

In all of these engines the fuel consumption, while comparatively 
good, does not in general run much below 1 lb. of oil per brake horsepower- 
hour. The compression does not, as a rule, run much above 60 or 70 lb. 
per square inch and usually is not so high in engines using hot-bulb igni- 
tion. The construction of these engines is practically the same as that 
of ordinary gas engines with the slight variations due to the vaporizer. 
In fact, a great many builders of engines up to 200 hp. make only slight 
modifications in their engines for the use of various fuels. The addition 
of the carburetter to the engine makes the ordinary producer gas engine 
fit for using gasoline. The addition of the vaporizer converts it into a 
kerosene engine. Otherwise the details are not modified in any way. 

In 1893 Dr. Rudolf Diesel pubhshed a book entitled "The Theory 
and Construction of the Rational Heat Motor," in which he described 
a new engine with the following characteristics: First, the production of 
the highest temperature of the cycle not by and during combustion, but 
before and independently of it entirely by mechanical compression of the 
air. Second, the gradual introduction of a small and carefully regulated 
quantity of finely divided combustible into the highly compressed and 



INTERNAL-COMBUSTION ENGINES 



427 



heated air, in such a way that no increase of temperature takes place and 
all the heat generated is at once carried off by the expansion of the gases 
of combustion. Third, introduction of a large excess of air while main- 
taining a proper combustion of the fuel. 




Fig. 235. — Section Busch-Sulzer Bros. Diesel engine. 



This paper created great interest among engineers because of the 
almost revolutionary ideas which it contained. Dr. Diesel in his first 
proposals attempted to compress the air isothermally to pressures exceed- 
ing 250 atmospheres. . This he soon found to be impossible of achieve- 
ment and he modified his motor by using adiabatic compression to around 
60 atmospheres. He also proposed using powdered coal as a fuel, but 



428 



ENGINEERING OF POWER PLANTS 



soon had to give this up because of the impossibility of getting rid of the 
ash which in a very short time stopped the working of the engine. The 
Diesel motor made very little progress from the date of its invention 
until about 1898 when small-sized engines of this type were put on the 
market by a number of manufacturers. 

The Diesel engine at first was built on the ordinary four-cycle prin- 
ciple. Of late years, however, the two-cycle engine has been rather 
largely built, an auxiliary air pump being introduced to provide proper 
scavenging. 




Fig. 236.— Sulzer Bros. Diesel engine, 1000 b.hp. 



Although there have been many variations introduced by manufac- 
turers, nearly all are today confining their attention to the standard 
Diesel principle with compression in the working cylinder up to 500 lb. 
per square inch (1,000°F.), using a multiple-stage air pump to provide 
the injection air at 600 to 850 lb. per square inch. 

The extremely high pressures and temperatures of the Diesel system 
have put a limit to the cylinder diameter at about 30 in., which corre- 
sponds to an approximate cylinder output of say 400 hp. at 150 revolu- 
tions with four-cycle practice. It does not seem advisable to use more 
than six cranks on account of shafting difficulties and today the largest 
motors of this type might have 800 hp. per crank or 4,800 hp. for a six- 
cylinder engine. This power may be nearly doubled by the adoption of 
the two-cycle system. 



INTERNAL-COMBUSTION ENGINES 429 

The four-cycle type of engine seems to be preferable for small sizes, 
although difficulties with the exhaust valve are of considerable importance 
and increase with the size of the engine. When the two-cycle type is 
used, in practically all large engines, the only serious difficulties have been 
from the inlet valves, which usually have to be gone over about once in 
from 6 to 8 weeks. The horizontal type of engine may be used in small 
sizes, but the best results on engines of any size have been obtained with 
the vertical engines. 

The DeLaVergne Co. in New York manufactures an engine designated 
as their F. H. type which operates on a variation of the Diesel principle. 
It is a four-cycle engine and compresses the air only to 250 to 300 lb., 
using a hot bulb to secure ignition. 




Fig. 237. — Three 1,000 B.H.P. Diesel type oil engines, Mcintosh Seymour Company. 

There are many methods of governing a Diesel engine, but in most 
cases the governing is done by bypassing the oil pump so that only the 
proper amount of oil for the work to be done is introduced into the 
cylinder. 

Among the auxiliaries required by a Diesel engine is an air compressor 
which must be of the two-stage type and have four valves. There must 
be an adjusting device to regulate the amount of air and it is customary 
to supply storage tanks, usually of the Mannesmann bottle type, in which 
the air is kept at a pressure of from 750 to 1,000 lb. 

The regulation of the air pressure for the engine at light loads is done 
by hand, otherwise the large amount of air admitted with the small charge 
of fuel might prevent ignition. 

It has been noted that the results of chemical analyses of different 
fuels do not furnish sufficient exact information regarding their suita- 



430 



ENGINEERING OF POWER PLANTS 



bility for use in the Diesel engine. This suitabihty can apparently only 
be determined by actual test. Two fuels of similar chemical analysis 
may give widely different results in the engine. There is a large selec- 
tion of cheap fuels available, such as crude mineral oil, mineral-oil 
residue and gas oil, that is, the intermediate products from oil re- 
fineries from which benzine and kerosene have been distilled, and the 
tar oils, tar from the water gas machine, byproducts from the distilla- 
tion of coal and paraffin, wood tar and paraflin oils. When tar is 
used, a small amount of gasoline is first injected to insure operation 
before the engine is warmed up. 

With such a choice of fuels it is probable that the Diesel engine will 
prove a favorite motor in many localities. 





Corapresssd 




Fig. 238- — Types of oil-engine vaporizers. 

Piston speeds of 600 to 1,000 ft. per minute are used. Speeds lower 
than 200 ft. per minute are not advisable on account of the leakage and 
difficulties with compression. 

An interesting development in the Diesel engine field is the adaptation 
of the Oeckelhauser type of engine to the Diesel principle. This has been 
done by Prof. Junkers, who has obtained 1,000 hp. from a single cylinder 
by his construction. In this engine three balanced cranks and connecting 
rods are used and the cylinders have no heads. Two pistons opposed to 
each other shde back and forth in the cylinder uncovering the exhaust 
ports at the ends of the stroke, the pumps being driven from the crossheads 
similarly to the ordinary marine steam engine. These engines are being 
built in the tandem type for marine use and promise to be of great im- 
portance, particularly for freighters whose principal business is oil carry- 
ing. The practical limit of cylinder dimensions for this type of engines 



INTERNAL-COMBUSTION ENGINES 



431 



will be much in excess of the 30-in. limit of the ordinary type of engine 
and with present materials there is little doubt that a 60-in. cylinder of 
72-in. stroke could be constructed today with good results. Fullager 
has also built engines of this type. 




Fig. 239. — Werkspoor 1100 b.hp. marine Diesel engine. 



At present the largest Diesel engines for land service are four-cylinder 
engines of approximately 2,400 b.hp. These engines are running for 
electric-light service with admirable results on a guaranteed oil consump- 
tion not to exceed 0.4 lb. of oil per brake horsepower-hour. They are of 
the two-cycle type. Four-cycle engines have an oil consumption of 



432 



ENGINEERING OF POWER PLANTS 



practically 90 per cent, of this figure, or about 0.36 lb. of oil per brake 
horsepower. 

The thermal efficiency of these engines is between 30 and 40 per cent. 
Twenty-five to 30 per cent, of the heat is carried away in the cooling 
water and the rest in the exhaust gases. 

COST OF FOUR-CYCLE DIESEL ENGINES 



Horsepower 


Engine, f.o.b., dollars 


Cost per horsepower, f.o.b., 
dollars 


100 


7,700 


77 


200 


12,600 


63 


300 


17,100 


57 


400 


21,600 


64 


500 


■ 26,500 


53 


600 


30,000 


50 


800 


39,200 


49 


1,000 


48,000 


48 



About 20 per cent, of the waste heat may possibly be utiUzed for heat- 
ing purposes and the claim is made that if a proper utilization of this heat 
be obtained the efficiency of the Diesel unit might be brought up to about 
80 per cent. 

The cost of two-cycle engines of large size is somewhat less, approxi- 
mately $35 to $40 per horsepower for engines of 1,000 hp. 

Foundations will cost from $2.50 to $4 per horsepower. 

Erecting labor will cost from $2 to $3 per horsepower. 
Summary of General Data on Diesel Engines. — 

Size: 

Smallest 6^ by S^i, two-cycle, four-cylinder, 110 b.hp. for four cylinders. 
Largest 32.2 by 39.4, two-cycle, one-cylinder, 1,250 b.hp. for one cylinder. 

Weight: 

250 to 500 lb. per horsepower in United States. 

Speed : 

150 to 250 r.p.m. Submarine service 350 to 550. 
600 to 900 ft. per minute piston speed. 

Mechanical Efficiency: 

Per cent, rated load 30 50 75 100 120 

Mechanical efficiency 43 62 70 75 78 

Thermal Efficiency: 

Per cent, rated load 50 75 100 120 

Thermal efficiency 25 30 31 30 



INTERNAL-COMBUSTION ENGINES 433 

Economy : 

Per cent, rated load 30 50 75 100 120 

Pounds, oil per brake horsepower-hour 

(Test) 0.71 0.55 0.46 0.43 0.44 

Pounds, oil per brake horsepower-hour 

(Mfgrs. guarantee) (Oil, 18,000 B.t.u. 

perpound 0.60 0.53 0.50 

Pressure for Spray: 

800 to 1,100 lb. per square inch. 
Air Required: 

16 to 34 cu. ft. free air per brake horsepower-hour. 
Power for Compressor: 

4 to 7 per cent, of engine power. 
Cooling Water: 

0.4 to 1.2 cu. ft. per brake horsepower-hour. 
Temperature Cooling Water: 

ISO"* to 140°F., max. 180°F. 
Lubricating Oil: 

1.25 gal. per 1,000 hp.-hr. 
Attendance : 

One man to 1,000 to 1,500 hp. 
Life and Repairs: 

Uncertain. 

The Humphrey Pump. — Probably no single power-plant development 
has attracted more widespread attention during the past few years than 
the Humphrey pump. The operation of this device as described by 
Messrs. Potter and Trump in Practical Engineer, Feb. 15, 1915, is as 
follows : 

"Operation of the Humphrey gas pump is similar to the four-stroke Otto 
cycle with the exception that in this pump there is complete expansion, whereas 
in the Otto cycle the losses from exhaust taking place under a high back-pressure 
are considerable. 

"To start the pump, the proper mixture of air and gas is forced into the 
cylinder by a small gas-engine-driven air compressor of the two-cylinder type, 
one cylinder pumping air and the other gas. Two separate systems of ignition 
are furnished, one consisting of special spark plugs operated from storage bat- 
teries and the other from an electric generator. 

"After the proper mixture of air and gas is in the cylinder, all the valves 
being closed, the charge is exploded by an electric spark, directly over the surface 
of the water, no piston or moving parts being used, and the increase in pressure 



434 



ENGINEERING OF POWER PLANTS 



resulting therefrom drives the water in the pump head downward, setting the 
whole column of water in the play pipe in motion. This column of water acquires 
kinetic energy during the period when work is being done upon it by the expand- 
ing gases. By the time these gases have expanded to atmospheric pressure, the 
water in the play pipe is moving at a high velocity, and as the motion of this 
column of water cannot be suddenly arrested, the pressure in the explosion 
chamber falls below atmospheric, when both scavenging and water valves open. 
A certain amount of water enters through the suction valves, most of which fol- 
lows the moving column in the play pipe, while the rest rises in the explosion 
chamber. To assist the scavenging action, a certain amount of air is admitted to 
the explosion chamber to mix with the spent gases. 

''Most of the kinetic energy in the moving column is expended in forcing 
water into the surge tank, and, as soon as the column of water in the play pipe 
comes to rest, it starts to move back toward the pump, gaining velocity until the 
water reaches the level of the exhaust valves, which are shut by constriction and 
impact. A certain quantity of the burned products mixed with the scavenging 




Fig. 240. — Humphrey pump. 



Fig. 241. — Valve gear, 
Humphrey pump. 



air is now imprisoned in the cushion space and the kinetic energy of the moving 
column is expended in compressing this to a much greater pressure than that due 
to the static pumping head. 

''As a result of the energy stored in these entrapped gases, the column of 
water is again forced outward; the pressure in the gas head is again reduced below 
atmospheric pressure, when a fresh charge of gas and air is drawn into the explo- 
sion chamber. Again the column of water returns and compresses the charge of 
gas and air which is then ignited to start a fresh cycle of operation. 

''Primarily, the period of cycle of the pump is determined by the length of 
the reciprocating column of water in the play pipe. This motion is similar to the 



INTERNAL-COMBUSTION ENGINES 



435 



swing of the pendulum of a clock, and its period of vibration is governed by the 
length of the water column in the same way as is the period of swing of a pendulum 
by its length. As a general rule, assuming the column to be of uniform section, 
the period of vibration is almost proportional to the square root of the length of 
the water column." 

Although extensive installations of this pump have been made in Europe and 
in Egypt, a brief description of one of the first plants to be installed in the United 
States is recorded by the same writers in the article mentioned as follows: 

*'In reporting upon the project to irrigate certain lands in Texas along the 
Rio Grande, extending from Del Rio to within 10 miles of Eagle Pass, the engi- 
neers employed had to decide between a gravity system involving the construc- 
tion of a supply canal some 16 miles long to water approximately 12,000 acres 
of land, and a pumping project to irrigate at once some 6,700 acres and to be 
extended to meet future needs. 




Fig. 242. — Diagram of Humphrey-pump installation. 

"Tentative plans and reports showed that the supply canal of the gravity 
project could be constructed for about $300,000 with an annual expense for fixed 
charges, maintenance and operation of approximately $40,000 irrespective of the 
use made of the canal. On the other hand, it was found the pumping project 
could be built for $60,000 and would entail an annual expense for fixed charges 
and depreciation of $6,000, and for maintenance and operation, $7,700. As the 
pumping project appeared so much more attractive financially than the gravity 
projects, its adoption was recommended. 

"The pumping engine selected is made under Humphrey and Smyth patents by 
the Humphrey Gas Pump Co., Syracuse, N. Y., and is guaranteed to pump not 
less than 20,000 gal. per minute against a static head of 37 ft. As it is believed 
that it will deliver in the neighborhood of 30,000 gal. per minute, all structures 
have been designed accordingly. The thermal efficiency of this pump is guaran- 
teed by the manufacturer to be not less than 20 per cent, of heat energy in the 
gas turned into work on the water when using producer gas having a heat value 
of not less than 100 B.t.u. per cubic foot. The Del Rio pump will make between 
12 and 20 complete cycles per minute." 

Reported test figures for an installation near London, using producer 
gas from anthracite, show: 



436 ENGINEERING OF POWER PLANTS 

Efficiency of gas plant, not including fuel used by auxiliary 

boiler, per cent 82 

Anthracite per water horsepower-hour pounds (guaran- 
tee was 1.1 lb.) 0.796-0.957 

Thermal efficiency based on water pumped, per cent 22-27 

Gas Turbines. — There may be three varieties of the gas turbine: first, 
the air turbine in which air is the working fluid and the furnace is outside 
the system. This turbine is analogous to the hot-air engine and may or 
may not have regenerative features. The air turbine is a toy and can 
never be of importance, because of the impossibihty of transmitting the 
heat to the air at a sufficiently rapid rate and because of the excessive 
size of the pumps and other auxiliaries. The theoretical efficiency could 
never exceed 10 per cent, and might be as low as 3 per cent. The com- 
mercial efficiency would be considerably lower. Second, the gas turbine 
in which gas alOne is used, predicating an inside furnace, compressors, 
regenerators and other complications. This turbine has more possibili- 
ties and an efficiency of 30 per cent, might theoretically be obtained. 
The size of the apparatus is large and the power used by the pumps be- 
comes prohibitive, if an attempt at high pressures is made. High tem- 
peratures are necessary for economy and the experimental apparatus has 
usually burned up or fused before a test could be obtained. Third, the 
steam and gas turbine in which water is injected to reduce the temperature 
and increase the efficiency of the apparatus. The steam and gas turbine 
may attain an efficiency equal to the engine, or say about 35 per cent., 
but this efficiency is dependent very largely on the furnace temperature. 
At 500°F. the theoretical efficiency is 3 per cent.; at 1,000°F., 12 per cent,; 
at 1,500°F., 20 per cent.; and at 2,000°F. around 27 per cent. The water 
injection helps to carry off the heat and by regeneration these efficiencies 
might be somewhat increased. 

There are 10 or 12 gas turbines of various kinds running at the present 
time. The economy, however, is not good, and in no case have real tests 
been reported. One of the latest machines, intended for 1,000 hp., built 
by Brown, Bouverie and Co. for the inventor, Holzworth, has been run 
somewhat successfully, but his published tests are not in a shape to quote. 
His machine is an air-cooled gas turbine, the air is admitted at atmos- 
pheric pressure, the gas is compressed in a centrifugal blower, while an 
exhaustor furnishes the vacuum. These two fans are driven by a steam 
turbine using steam made from the exhaust gases in a regenerator. Al- 
most any kind of gas or oil fuel may be used, and he even used powdered 
Cannel coal in one of his tests. The 1,000-hp. unit weighs 25 tons and 
consists of a number of explosion chambers, each provided with valves, 
igniters and nozzle. The explosion chambers form the bedplate of the 
machine and the wheel is a two-stage impulse wheel with vertical shaft. 



INTERNAL-COMBUSTION ENGINES 437 

PROBLEMS 

87. If a 600-lip. gas engine requires 11,500 B.t.u. per horsepower-hour at full load, 
how many cubic feet of each of the following gases will be required per hour when the 
engine is developing (A) 300 hp.; (B) 100 hp.? 

(a) Natural gas. 

(6) Illuminating gas. 

(c) Up-draft producer gas. 

(d) Down-draft producer gas. 

(e) Blast-furnace gas. 

88. Given a 100-hp. gas engine consuming 1,200 cu. ft. of natural gas per hour at 
full load with the barometer reading 29.35 in. and under a manometer pressure of 7 in. 
of water with the temperature of the gas 85 °F. 

The heat value of the gas is 940 B.t.u. per cubic feet as measured. Determine : 
(a) The consumption of standard gas (60°F. and 30 in. Hg.) per horsepower-hour. 
(6) The B.t.u. per horsepower-hour. 

(c) The thermal eflBciency (based on the heat value of the gas and the brake horse 
power). 

(d) The amount and cost of water required by this engine for one month's oper- 
ation (26 days, 10 hr. per day). 

89,. A customer purchased a 200-hp. gas engine guaranteed to consume not over 
3,300 cu. ft. of illuminating gas per hour when running at full rating. 

When he received his gas bill for the first month amounting to $566 he felt that it 
was excessive and entered a protest. The records showed that the direct-connected 
D.C. generator had developed 17,800 kw.-hr. for the month, operating with uniform 
load 9 hr. a day for 26 days. Cost of gas $1 per 1,000 cu. ft. 

1. Based on the guarantee was he justified in his protest or was the bill correct? 

2. If the bill is incorrect, how much is it out? 

90. Another customer with a 200-hp. gas engine guaranteed to consume not over 
2,200 cu. ft. of natural gas per hour when running at full rating protested his bill of 
$110 for the month. The records showed that the direct-connected D.C. generator 
had developed 17,800 kw.-hr. for the month, operating with uniform load 9 hr. a day for 
26 days. Cost of gas 30 cts. per 1,000 cu. ft. 

1. Based on the guarantee was he justified in his protest or was the bill correct? 

2. If the bill is incorrect, how much is it out? 

91. If running under normal conditions, how many gallons of gasoline should a 
250-hp. gas engine consume per 10 -hr. day when developing: 

(a) 50 hp. 

(b) 80 hp. 

(c) 100 hp. 

(d) 175 hp. 

(e) 225 hp. 

92. An acceptance test of a 100-hp. gas engine operating on illuminating gas shows 
it to be consuming 1,810 cu. ft. of gas per hour at a load of 75 b.hp., the gas being 
metered at a temperature of 70°F. and under a pressure of 3 in. of water above atmos- 
phere (barometer = 29.58). The heat value of the gas at standard conditions (60°F. 
and 30 in. barometer) is 600 B.t.u. per cu. ft. 

The engine is guaranteed to give a full-load thermal efficiency (on b.hp.) of 25 per 
cent. 

Would the test results justify claims of failure to meet the guarantee? 
What gas consumption (as metered) should have been expected? 



438 ENGINEERING OF POWER PLANTS 

93. Given a 150-kw. gas power plant with direct-current generator, direct-con- 
nected to a four-cycle gas engine. Fuel, natural gas. 970 B.t.u. per cubic foot. 

Determine the test economy of the plant in terms of cubic feet of gas per kilowatt- 
hour output at the switchboard if the demand on the plant is as follows : 

6.00 a.m. to 8.30 a.m. 100 kw. 

8.30 a.m. to 10.30 a.m. 150 kw. 

10.30 a.m. to 3.00 p.m. 70 kw. 

3.00 p.m. to 7.00 p.m. 125 kw. 

7.00 p.m. to midnight 90 kw. 

Midnight to 6.00 a.m. • 60 kw. 

94. A manufacturer is considering the installation of a generating set to deliver a 
rated load of 200 kw. (direct-connected). Three types of installations are under 
consideration : 

(A) A simple, high-speed, non-condensing steam engine and direct-connected 
generator, hand-fired, water-tube boilers (two in service, one in reserve), closed feed- 
water heater, and feed pumps. 

(B) A four-cycle, two-cylinder, Diesel-type oil engine with direct-connected 
generator, to operate on crude oil at 3 cts. per gallon. 

(C) A four-cycle gas engine with generator, to operate on natural gas at 20 cts. per 
1,000 cu. ft. 

Coal used in the steam plant will be bituminous coal costing $3 per ton. Water 
costs 40 cts. per 1,000 cu. ft. 

A building to house the plant is available, without cost, but foundations, stack, 
etc., must be provided. 

The plant will carry full load 10 hr. per day, 308 days per year. 

Estimate the total installation cost, the total yearly operating costs including 
fixed charges, and the resultant cost per kilowatt-hour generated. 



CHAPTER XXII 
PRODUCER GAS AND GAS PRODUCERS 

Producer Gas. — Gas of some kind and quality can be made from 
almost anything that will burn and nearly all gases used for power, heat- 
ing and lighting, with the exception of natural gas, are derived from the 
combustion of solid fuels or the vaporization of liquid fuels. From the 
standpoint of practical convenience and economy the fuels commercially 
employed for making producer gas are generally coal, coke, charcoal, lig- 
nite and peat, although wood, sawdust, straw, oil, etc., may be advan- 
tageously used under certain conditions. 

In the most familiar process of gas making, namely the nianufacture 
of coal gas, the coal is subject to destructive distillation. The resulting 
gas is high in illuminating qualities and has a relatively high heat value 
per cubic foot. In this process there is a valuable byproduct in the form 
of coke which finds a ready market at a remunerative price. 

In another process of gas making from coal a limited supply of air, 
with or without water vapor or steam, is passed through a thick fuel bed. 
By the proper regulation of this air supply a partial or incomplete com- 
bustion of the fuel is maintained resulting in the gradual consumption of 
the entire combustible portion. Instead of having a large coke yield as 
a byproduct, as in the former process, the coke is utilized in the gas mak- 
ing. Gas made according to this latter method is known as producer 
gas and the apparatus in which the gas is developed is called the gas 
producer. 

Composition of Producer Gas. — In the manufacture of any gas it 
is found that its definite composition will vary considerably from time 
to time unless the details involved in the gas production are definitely 
controlled. 

The essential constituents are found in all kinds of fuel gas but in 
such widely different proportions that the gases resulting from the differ- 
ent systems of manufacture vary greatly in their range and manner of 
commercial application. 

The heat value of any gas is determined by the proportion of com- 
bustible gases present in any mixture and by the relative percentage of 
each of the individual gases. The non-combustible gases of course add 
nothing to the heat value but rather act in the opposite direction, that is, 
as diluents. 

439 



440 



ENGINEERING OF POWER PLANTS 



These combustible and non- combustible portions usually embody 
the following constituents in varying proportions in the different types 
fo gas: 



(1) Combustible gases 
Hydrogen, H2 
Carbon monoxide, CO 
Methane, CH4 (marsh gas) 
Ethylene, C2H4 



(2) Non-combustible gases 
Nitrogen, N2 
Carbon dioxide, CO2 
Oxygen, O2 



Not only is there a wide variation in the composition of various types ,j 

of gases, but considerable variation will often be found in gases of the ! 

same general type. j 

Typical analyses of producer gas are: 



Composition by Volume, Per, Cent. 



From 
anthracite 



From 

bituminous 

coal 



From 
lignite 



From 
peat 



From 
wood 



IJP-DRAFT PLANTS 



Hydrogen, H2 

Carbon-monoxide, CO 

Methane, CH4 

Ethylene, C2H4 

Oxygen, O2 

Carbon dioxide, CO2. . 
Nitrogen, N2 



15 
22 



0.0 
0.0 
0.3 
5.5 
56.0 

100.0 



12.90 


13.74 


18.50 


18.28 


18.72 


21.00 


3.12 


3.44 


2.20 


0.18 


0.17 


0.40 


0.04 


0.16 


0.00 


9.84 


10.55 


12.40 


55.60 


53.22 


45.50 


100.00 


100.00 


100.00 



4.0 

13.6 

8.0 

0.0 

0.0 

12.9 

61.7 

100.0 



Hydrogen, H2 '. 

Carbon monoxide, CO , 

Methane, CH4 

Ethylene, C2H4 

Oxygen, O 

Carbon dioxide, CO2. . 
Nitrogen, N2 



Down-draft plants 



12.01 


14.76 


10.19 


21.05 


16.01 


16.91 


0.49 


0.98 


0.66 


0.01 


0.00 


0.06 


0.13 


0.01 


0.41 


6.22 


11.87 


10.94 


60.09 


56.37 


60.83 


100.00 


100.00 


100.00 



Besides the constituents mentioned, fuel gases often contain vapors 
which do not appear in the analysis, but which may prove useful or 
detrimental in the commercial application of the gas. Many of these 
vapors are hydrocarbon compounds, the most famihar of which and the 
most important are tarry matters. 



i 



PRODUCER GAS AND GAS PRODUCERS 441 

As is readily seen, the simplest producer gas is made by passing dry 
air through a thick bed of carbon, commercially either charcoal or coke. 
If a producer be filled with charcoal or coke and a fire be kindled in the 
lower portion then as the dry air enters from below the oxygen of the air 
will combine with a limited portion of the carbon in the incandescent 
zone thus supporting the combustion and developing a CO2 gas. If now 
this carbon dioxide gas be passed through the deep bed of charcoal or 
coke (carbon) above the burning zone, the oxygen and carbon tend to 
unite to form carbon monoxide, CO, if the proper temperatures prevail. 
This gas is the simplest of producer gases, but it is low in heat value, and 
difficult to produce on an economical commercial basis. The usual pro- 
cedure in producer gap making is to utilize coal as the fuel and to add a 
certain amount of steam with the air. This steam not only has the effect 
of enriching the gas but also tends to reduce the fuel-bed temperatures 
which otherwise may become too high for the successful generation of 
this gas. Steam, upon meeting an incandescent fuel bed, is decomposed 
so that the combination of carbon and steam is theoretically broken up 
into carbon monoxide and hydrogen (C + H2O = CO + 2H2). The 
enrichment of the gas from the steam is due to the additional hydrogen. 
It is also essential that sufficient care be exercised in the use of steam to 
prevent the chilling of the bed to such a point that the necessary decompo- 
sition cannot take place. The amount of steam that can be used to 
advantage is, therefore, limited. It is possible to maintain combustion 
with the air which is supplied and at the same time supply such a large 
amount of steam that its complete decomposition cannot follow owing 
to lack of temperature in the fuel bed. The result is usually an excess 
of carbon dioxide and the mechanical mixture of a certain portion of the 
steam still undecomposed with the gas issuing from the generator. 

When coal is used in place of coke there is usually considerable volatile 
material, especially in bituminous coals, which is distilled from the fresh 
coal at the top of the producer by the heat in the gas which passes up 
through the fuel bed. Besides this coal gas there is usually considerable 
tarry material given off by coal which may or may not be objectionable 
in the application of the gas according to the method of utilization. If 
these tarry products or hydrocarbon compounds are allowed to chill they 
may be very objectionable in certain types of plants owing to their tend- 
ency to clog pipe lines, valves, engine governors, etc. It is important, 
therefore, when this gas is to be used for operating engines that this tar 
be eliminated from the gas or be itself converted into a gas which may be 
utilized as a part of the regular output of the plant. The methods of 
handling these tarry products will be discussed later. 

As previously pointed out, carbon monoxide, hydrogen, ethylene and 
methane are desirable constituents in producer gas. The application of 



442 ENGINEERING OF POWER PLANTS 

the gas in various industrial uses depends somewhat upon the relative 
proportions of these different constituents. Gases with a high percentage 
of hydrogen may be well adapted to certain types of metallurgical appli- 
cation but for power purposes involving the use of the gas in internal- 
combustion engines it is found necessary to keep the percentage of hy- 
drogen within certain limits. For this reason the methods of operating 
producer plants for power purposes are often quite different from those 
applied when the gas is to be used for metallurgical work. 

As will be noted in the above analyses, oxygen usually appears in very 
small percentages. Nitrogen has no special effect but simply acts as a 
diluent. The third diluent, carbon dioxide, is an undesirable constituent 
in producer gas and the percentage present should always be the minimum 
possible with any given grade of coal or method ot manipulation. The 
chief objections to carbon dioxide in the gas are that it indicates the de- 
velopment of more heat than is required in the process of gas making; 
shows the presence of a larger percentage of nitrogen than would be the 
case with more perfect operation and also indicates that a certain portion 
of the carbon monoxide has been burned in the producer or that the thick- 
ness of the fuel bed was not sufficient to reduce the carbon dioxide evolved 
in the incandescent zone to carbon monoxide before leaving the producer. 
The principle causes of an excess of carbon dioxide are a thin incandescent 
fuel bed without sufficient depth of carbon to properly decompose the 
carbon dioxide produced in this incandescent bed and too low temperature 
in the fuel bed, usually due to an over-supply of steam. 

Types of Gas Producers. — Two distinct processes of making producer 
gas are in use — the up-draft process and the down-draft process. For 
commercial purposes these processes are applied by different manufac- 
turers in different ways resulting in the following four general types of 
producers: • 

(a) Up-draft suction producers. 

(6) Up-draft pressure producers. 

(c) Down-draft producers. 

(d) Double-zone producers. 

The Up-draft Suction Producer. — As originally manufactured the 
suction, or reduction of pressure below that of the atmosphere, was pro- 
duced entirely by the suction stroke of the engine. Today this reduction 
in pressure is more often produced by the introduction of a mechanical 
exhaustor, thus simplifying the operation. 

The operation of the engine-type suction plant is described below. 

As shown in Fig. 243 the essential parts of a suction-producer plant 
are the gas generator or furnace, the steam generator or boiler, and the 
gas cleaner or scrubber. A fire is made with shavings, wood, etc., on 
the grate of the gas generator, the air necessary for combustion being 



PRODUCER GAS AND GAS PRODUCERS 



443 



supplied by means of the blower shown at D. As soon as the fire is 
sufficiently kindled the fuel to be used for gas making — charcoal, coke or 
anthracite — ^is gradually charged into the producer. The blower for the 
air supply is driven by hand, or in large plants by electric or other power, 
until gas of sufficiently good quality to operate the engine is generated. 
The quality of the gas is roughly ascertained by means of a test-cock at 
which the gas is lighted. As soon as the test flame shows the right color, 
which can be readily determined after a little experience, the gas is turned 
into the engine. The smoke and poor gas developed during the early 
stages of combustion are discharged into the outside air by means of the 
purge pipe shown at ^. As soon as the engine is started, the blowing of 




Fig. 243. — Engine-type suction gas producer plant. 



the producer is stopped, and the necessary air for maintaining combustion 
is drawn into the base of the producer by means of the suction produced 
in the engine cylinder. 

If air alone is supplied, even in restricted quantities, the temperature 
of the fuel bed in the producer rises so high as to hinder the production of 
satisfactory gas. It is necessary, therefore, as previously stated, to cool 
the fuel bed by adding steam. The methods of producing this steam 
vary in detail in plants of different design, but the principles involved 
are essentially the same. 

At C is shown the steam generator or boiler for this particular type 
of producer. Steam at atmospheric pressure is generated by the heated 



444 



ENGINEERING OF POWER PLANTS 



gas, which leaves the producer at the point F on its way to the scrubber. 
The steam thus generated is picked up by the air supply passing into the 
base of the producer. The mixture of air and steam is then drawn up 
through the incandescent fuel bed. The oxygen of the air and the oxygen 
of the steam combined with the highly heated carbon in the lower part 
of the bed, producing complete combustion and developing carbon diox- 
ide. The gas thus formed passes up through a thick fuel bed above 
and the carbon dioxide is largely reduced to carbon monoxide. The 
hydrogen liberated by the decomposition of the steam greatly enriches 
the product. 

Scrubbing the Gas. — The gas after leaving the gas generator at the 
point F passes to the base of the scrubber G. The scrubber is usually a 







■■■ir£iaj^£L ^^^ Hfc 


si 


■H 


H 1 


i>f^^ 




DK ■ 


i£^°^^g 







Fig. 244. — Smith gas producer. 

cast-iron or sheet-steel tower in which dust, soot, tar and other im- 
purities are removed from the gas. As usually constructed it consists 
of a simple cylindrical shell filled with coke, over which water is sprayed. 
The dirty hot gas enters the base of the scrubber and flows upward; it 
is divided, in passing through the coke, into separate streams which are 
met by a fine water spray flowing in the opposite direction. The gas 
and the water are thus brought into intimate contact and the particles 
of dirt and other foreign matter carried by the gas are largely washed out. 
The wash water from the scrubber passes into a water seal shown at K, 
from which it overflows into the drain, or, in large installations, into a 
settling basin or reservoir. If the gas is to be used in an engine it is 
essential that it be thoroughly freed from gritty material in order to pre- 
vent scoring of the engine cylinders. It is equally important that tarry 



PRODUCER GAS AND GAS PRODUCERS 



445 



compounds be removed, in order to prevent clogging of the engine valves 
and governor. 

Owing to the fact that the draft of air and steam through the fuel 
bed is produced by the suction stroke of the engine, it is important that 
the resistance offered by the fuel bed, scrubber and connections should 
at all times be a minimum in order that the power from the engine avail- 
able for commercial use may not be too seriously reduced, by the demands 
for operating the producer plant itself. With this in view it is essential 




Fig. 245. — Smith gas producer plant. 

that the grate be kept free from the accumulation of ash and that clinker- 
ing in the fuel bed be reduced to a minimum. It should further be borne 
in mind that owing to this suction action of the engine any tarry products 
or other foreign matter that may have passed by the scrubber will be 
drawn directly into the engine valves. Any large amount of tar condens- 
ing and cooling in the valves or governor attachments of the engine tends 
to interfere with its successful operation. For this reason fuels containing 
large percentages of tar are not available for use in this type of suction 
producer. This of necessity restricts the fuels in regular use in these in- 



446 



ENGINEERING OF POWER PLANTS 



stallations to charcoal, coke and anthracite coal. Even with certain 
cokes and anthracite coals there is a slight tar production which has to 
be properly cared for. 

By the introduction of an exhauster of the Root or Gonnersville type 
the pressure through the gas-generating system may be maintained below 
that of the atmosphere without depending upon the suction stroke of the 
engine. The application of these exhausters is readily seen by reference 
to Figs. 246, 249, 250 and 252. 

The pressure on one side of the exhauster is, of course, negative and 
on the other positive. This arrangement makes possible the introduction 
of additional gas-cleaning devices and the possible use of bituminous coal 
and other tarry fuels. 




Fig. 246. — Charging floor Smith producer showing tar extractor. 

The largest single unit installed to date is an up-draft suction producer 
in which the reduction of pressure is maintained by an exhauster as shown 
by Figs. 245 and 246. 

The producer is of simple construction of sheet steel and channels. 
It is made on the sectional principle and can easily be enlarged by the ad- 
dition of one or more sections. As operated, the plant shown by the cuts 
has a fuel-bed area of 210 sq. ft. and burns about 2,750 lb. of Illinois coal 
per hour. 

Owing to the fact that the fuels generally used in the engine-type suc- 
tion plants are high in price, the installations of this type, although nu- 
merous, are of comparatively small power, seldom exceeding 300 hp. per 
unit and in the majority of cases not exceeding 100. 



PRODUCER GAS AND GAS PRODUCERS 



447 



The Up-draft Pressure Producer. — The pressure producer develops 
its gas under slight pressure (usually 2 to 8 in. of water) . This pressure is 
produced by means of steam introduced through the blast pipe shown in 
the cut. The air enters the producer through this same pipe, being 




Fig. 247. — Up-draft pressure gas producer. 

drawn in by means of induced currents produced by the steam. The 
steam is supplied at a pressure of from 40 to 80 lb. by an auxihary boiler. 

In this type of producer it is necessary to carry an ash bed deep enough 
to protect the blast pipe. 

On top of .this ash bed is the incandescent zone and above this 



448 



ENGINEERING OF POWER PLANTS 




PRODUCER GAS AND GAS PRODUCERS 449 

the deep fuel bed, supplying the carbon for reconverting the CO2 gas 
into CO. 

The other essential parts of the up-draft pressure producer-gas plant 
are a preheater for heating the air entering the producer by means of the 
sensible heat of the hot gas from the producer; a scrubber for cleansing 
the gas; a tar extractor and tar drips; a pressure regulator; and sometimes 
a purifier for removal of sulphur from the gas. The elevation of such a 
plant is shown in Fig. 248. 

The Bown-draft Producer. — By the mechanical extraction of tar a 
large part of the heat value of the gas is lost. As already stated, this may 
not be a serious matter in plants where the sale of the tar for commercial 
uses brings a good financial return, but in installations where the tar is 
thrown away the loss is sufficiently serious to warrant the attempt to 
devise some means of converting this tar into a gas of suitable quality 
for engine use. Attempts have been made to accomplish this result by 
manufacturers in this country and abroad, and the success attained has 
been sufficient to warrant the building of such plants on a commercial 
basis. 

Operation of a Typical Plant. General Description. — A typical plant 
of this character manufactured in the United States is shown in Fig. 249. 
This plant consists of two gas generators made of steel shells with firebrick 
linings. As in the types previously mentioned, the essential features of 
this type of plant are the gas generators or producers, the steam generator 
or boiler, the gas-cleaning apparatus or scrubbers (both wet and dry), 
the gas holder or receiver, and the necessary auxiliary piping, etc. 

In operating the producer plant the gas generators are charged with 
coke to a height of 3 or more ft. above the grates, and lumps of coal about 
4 in. in diameter are added on top of the coke to the depth about 6 in. 
A wood fire is then kindled on top of this charge. The valves in the pipes 
at the base of the producers leading to the boiler being open, the exhauster 
a is started and the entire portion of the plant to its left is thus placed 
under suction. The air for supporting combustion is drawn in through 
the charging doors shown above the operating floor at b, downward 
through the fuel bed and pipe line into the base of the boiler, up through 
the boiler tubes and pipe line to the base of the scrubber, and then up 
through the scrubber into the exhauster. From the exhauster the gas 
is under pressure and may be sent through the dry scrubber c into the 
gas holder, or by simply opening the valve may be sent through the 
purge pipe d, into the outside air. When starting the fire, smoke and 
impure gas are diverted through the purge pipe until such time as the 
test flame shows the gas is suitable for turning into the holder. 

After the coke has become incandescent and the fire in the upper 
portion of the fuel bed well established, green fuel is added through the 



450 



ENGINEERING OF POWER PLANTS 




PRODUCER GAS AND GAS PRODUCERS 451 

charging doors b as the condition of the fire and the quahty of the gas 
require. 

The steam required by the plant is generated in the tubular boiler e 
by the heat of the gases as they pass from the generator to the scrubber. 
Sufficient heat is furnished in this manner to supply steam at 60 or 80 
lb. pressure in the average plant of this type, although occasionally it is 
found best to install an auxiliary boiler. The steam which enters the 
producer above the fuel bed at the point / mingles with the air entering 
at h and the mixture passes down through the fuel bed, as previously 
outlined. 

The gas is cleaned by the coke scrubber, although in this particular 
type of plant the scrubber is fitted with partitions or shelves, upon which 
the coke is placed. The water spray which meets the ascending gas 
currents is show n at ^. The upper portion of this scrubber is generally 
filled with excelsior, thus making a dry scrubber which removes consider- 
able moisture from the gas besides impurities. The additional dry scrub- 
ber, shown at c, is also filled with excelsior, and consists of two chambers, 
with valve connections so arranged that either chamber may be bypassed 
for cleaning. 

Conversion of Tarry Vapors into Fixed Gases. — By this down-draft 
process the hydrocarbon compounds and volatile material distilled from 
the green coal in the top of the fuel bed are drawn into the incandescent 
zone, where the tarry material is to a certain extent converted into a 
fixed gas. The completeness of the conversion is determined by the coal 
used, the conditions of the fuel bed, and the method of operating. Some- 
times the process is exceedingly satisfactory and the tarry products are 
practically all transformed into a good grade of gas; at other times a 
portion of this material is transformed into gas and a portion is burned 
in the incandescent zone. One of the criticisms of the system is that at 
some plants much lampblack is produced. Although this may cause no 
serious results so far as the operation of the engine is concerned, yet lamp- 
black is a disagreeable substance to handle in any quantity and tends to 
collect in every nook and crevice. If it is not properly removed when 
coals containing a high percentage of sulphur are used there is a possi- 
bility of a weak solution of sulphuric acid forming in certain portions of 
the plant and gradually eating away any iron or steel with which it may 
come into contact. 

"Shooting'^ the Fuel Bed. — After operating this plant for a few hours 
by the method described, the fuel bed in each of the generators gradually 
becomes clogged with tarry matter, soot, dust, ash, etc., and the suction 
required of the exhauster becomes excessive. If the plant is clean this 
suction amounts to possibly 5 or 6 in. of water, and gradually increases 
as the fuel bed becomes clogged. In the majority of plants it is not 



452 



ENGINEERING OF POWER PLANTS 



deemed wise to allow the suction to exceed about 20 in. of water, although 
there are plants in daily operation in which 60 in. are carried without 
difficulty. When this suction becomes excessive, it is necessary to clean 
the fuel bed. This cleaning, which must be done without stopping the 
plant, is carried on as follows: 

Suppose the fuel bed in the generator marked A, Fig. 249, requires 
cleaning. The charging doors b, h are closed, then the valve connecting 
the base of the producer A to the boiler is also closed by means of a wheel 
manipulated from the operating floor, and the steam entering the top of 
the producer is cut off and steam at full pressure, namely, 60 to 100 lb., is 
discharged. into the base of the producer just below the grate. This high- 
pressure steam rushing through the fuel bed tends to dispel the tar, soot, 
dirt, ash, and other foreign material. The process is called ''shooting.'' 
During the process the current through the fuel bed is, of course, reversed; 
that is, made to flow upward instead of downward. In the shooting a 
jet of live steam is turned upon an incandescent fuel bied, and a water gas 
is formed which is quite different from the gas produced during the down- 
draft operation of the plant. The heat value of this gas averages about 
200 B.t.u. per cubic foot instead of a little over 100 B.t.u., which is the 
heat value of the gas normally made by the producer. During the process 
of shaking up and cleaning the fuel bed the water gas is passed up through 
the fuel bed into the top of the generator A; through the bypass pipe 
behind the boiler, shown at h ; down through the fuel bed of the generator 
B; and then on through the boiler and scrubber to the exhauster, as in 
the normal working of the plant. The method of cleaning generator B 
is the same, except, of course, that the operation of the two generators 
is in reverse order. 

Utilization of Water Gas. — The gas produced during the cleaning 
process, high in hydrogen and of relatively high fuel value, differs so 
materially from the gas regularly made that many operators of down- 
draft plants find it inadvisable to mix the two gases, and provide two 



DESCRIPTION OF FIG. 250. 


1. Air intake. 


22. 


Water trap. 


2. Producer. 


23. 


Sprayers. 


3. Fuel. 


24. 


Water supply for trap. 


4. Waste gas stack. 


25. 


Water drain for trap. 


5. Removable stack. 


26. 


Up-draft air connection. 


6. Center charging door. 


27. 


By-pass connection. 


7. Secondary vaporizer and Water-cooled top. 


28. 


Grate for supporting coke in wet scrubber. 


8. Side charging door. 


29, 


Wet scrubber. 


9. Mixture inlet. 


30. 


Scrubber sprays. 


10. Peek hole. 


- 31. 


Scrubber gas off-take. 


11. Vaporizer. 


32. 


Exhauster Del. gas to expansion tank and 


12. Vaporizer inspection hand hole. 




Engine. 


13. Vaporizer water supply. 


33. 


Drain. 


14. Vaporizer overflow gauge. 


34. 


By-pass and up-draft connection. 


15. Top of ash bed. 


35. 


Waste gas stack. 


16. Ash pier concrete. 


36, 


Auto. By-pass valve (sending surplus gas back 


17. Foundation piers. 




to scrubber). 


18. Waterseal pit. 


37. 


Gas to engine. 


19. Gas off -take (from prod.). 


38. 


Combined expan. tank and purifier. 


20. Sprayer column No. 1. 


39. 


Scrubber drain (sealed^. 


21. Sprayer column No. 2. 


40. 


Baffle plate. 



PRODUCER GAS AND GAS PRODUCERS 



453 




Baa 



^.e 



454 



ENGINEERING OF POWER PLANTS 



gasometers, one for the regular producer gas, or air gas, as it is sometimes 
called, the other for the gas generated during the shooting process, which 
is generally termed water gas. The discharge of these two types of gas 
to their respective gasometers is controlled by the operator on the charg- 




FiG. 251. — Westinghouse double-zone gas producer. 

ing floor. The number of times a bed should be shot during the day de- 
pends largely upon the character of the fuel used, the demands on the 
plant, and the methods of manipulation. It is not deemed desirable to 
utilize the water gas in some plants used only for power purposes, and the 



PRODUCER GAS AND GAS PRODUCERS 



455 



gas is discharged into the atmosphere through the purge pipe. In certain 
plants with high-grade fuels and proper manipulation it is necessary to 
shoot the bed only two or three times a day. As the period required for 
the operation is not over a minute or two, the resultant loss from the 
discharge of gas through the purge pipe amounts to very little. In other 
plants where producer gas is used for heating, annealing, tempering, forge 
work, etc., in addition to its use for the development of power, it is ad- 
visable to generate as much of the higher heat-value water gas as possible. 
To this end, the bed is shot as often as may be done without chilling the 
incandescent zone below an efficient temperature. 

Single generator down-draft plants are now in use from which the 
ash may be withdrawn without shutting down the gas generator thus 
allowing continuous operation as shown by Fig. 250. 




Fig. 252. — Westinghouse double-zone gas-producer plant. 

The Double-zone Producer. — The double-zone producer is, as its 
name implies, a combination of the up-draft and down-draft principles. 
Two incandescent zones are maintained and the gas is withdrawn at the 
center or waist-line of the producer. The CO2 gas formed in both of 
these zones is thus drawn through the central coke zone where it is recon- 
verted to CO. After the initial fires are started and the plant in operation, 
the fresh fuel is charged at the top and the volatile matter drawn down 
through the upper incandescent zone where the hydrocarbons are either 
burned or converted into a fixed gas, thus destroying the tar. The cen- 
tral coke zone supplies the lower incandescent zone with fuel and in turn 
is maintained by the coke formed in the upper zone. Care in controlling 



456 



ENGINEERING OF POWER PLANTS 



the distribution of air to the upper and lower zones is required to insure 
the proper balance for continuous operation. 

Vaporizers. — As already pointed out steam is essential in producer-gas 
making. It is introduced with the air. In many plants it is generated 




Fig. 253. — Smith tar extractor. Capacity 250,000 cu. ft. per hour. 




Fig. 254. — Section of Smith tar extractor. 



by the sensible heat of the gases as shown in Fig. 243, but for the pressure 
plants it is usually generated in an auxihary boiler. For suction plants 
the steam is at atmospheric pressure or a little below this pressure, while 
in the down-draft plant of the type shown in Fig. 249, the steam pressure 



PRODUCER GAS AND GAS PRODUCERS 



457 



is in the neighborhood of 60 to 80 lb. This is also the usual pressure 
carried by the auxiliary boilers of the pressure-type installations. 

Scrubbers and Tar Extractors. — Ideas regarding the best method of 
cleaning the gas seem to vary greatly. At one extreme is a scrubber 
without coke or other solid material, completely filled with finely atomized 
water or fog, through which the gas passes. At the other extreme is a 
tall tower-like scrubber with the water pelting down in large drops or 
globules and supposedly beating the dust and dirt out of the gas. The 
ordinary practice, however, is to use coke-filled scrubbers and water spray. 

In passing through the scrubber the gas is more or less cleansed, de- 
pending on the character of the fuel used and the process of gas making. 
In the down-draft process additional scrubbers filled with excelsior are 
used for removing moisture and lampblack from the gas. For up-draft 




Fig. 255. — Details of a Smith tar extractor. 

The above is a photograph of the tar extractor for a 200-hp. producer. The previous illustration 
shows a section of this apparatus on a plane through the parallel axes of the tar extractor and gas line. 

Either of the two extractor heads may be cut in or out of service without affecting the operation of 
the plant. The heads are ported so that the gas passes through the extractor when its axis is parallel 
to that of the gas main, and when turned ninety degrees the extractor is out of service. In this illustrf\- 
tion the head on the left is out of service and the screens and holder, in which the glass-wool diaphragm 
is mounted, are dissembled. The coverplate is removed from the head on the right, showing the dia- 
phragm assembled and in place. 

plants using tar-producing fuels, some process of tar extraction must be 
introduced. The most common type of tar extractor removes the tar by 
centrifugal action, the extractor resembling a centrigufal pump. From 
the extractor the gas passes through tar drips to water-sealed pits. A 
liberal supply of water is required for this process, and the speed of rota- 
tion of the fan is of vital importance. 

I A recent form of static tar extractor^ requiring no water is shown in 
Figs. 253, 254 and 255. 
The descriptive paragraphs are from the manufacturers catalogue. 
1 For a complete description of this tar extractor see Transactions A.S.M.E., 



458 ENGINEERING OF POWER PLANTS 

Special Producer-gas Engine Conditions. — As previously stated, it is 
necessary in order to make producer gas suitable for use in an engine 
that it be thoroughly scrubbed and cleaned and that it be sent to the en- 
gine at a low temperature. By keeping the temperature low a given 
volume of gas contains a large number of heat units and, consequently, 
is capable of developing more power in the engine cylinder than the cor- 
responding volume of the weaker gas. Another advantage in sending 
the gas cold to the engine is the fact that there is no danger of any con- 
densation of tarry vapors or water vapor after reaching the engine cylin- 
der. This is probably a minor advantage as the engine cylinders are 
usually kept at a sufficiently high temperature to prevent any possibil- 
ity of such condensation even if the gas be delivered at a relatively high 
temperature. 

Producers for Metallurgical and Heating Purposes. — Producer gas 
has for years been extensively used in various types of furnaces in the 
manufacture of iron and steel. This use has become more and more 
general during the last few years. In districts where the steel mills have 
had an abundant supply of natural gas no necessity for a substitute has 
been felt and no incentive for economizing the fuel supply has existed. 
The supply of natural gas, however, is by no means unlimited — in some 
places it has failed altogether — and the time when it will no longer be 
available in large quantities is near. Large users of this remarkable 
natural resource have had to recognize these conditions and to hold them- 
selves in readiness to use artificial gas when the supply of natural gas 
becomes inadequate. The solution of the problem is found in the gas 
producer, and at the present time there are within the natural-gas regions 
large installations of gas producers used for the operation of openhearth 
furnaces. 

In the manufacture of producer gas for metallurgical processes the 
gas goes to the furnace directly from the producer without any cooling 
or cleaning. It therefore enters the furnace highly heated, carrying with 
it all volatile hydrocarbons and tarry matter, as gases or vapors, and these 
add much to the heat value of the gas. The simplicity of the gas-pro- 
ducer equipment required where cleaning of the gas is not essential is 
shown clearly in Fig. 241. The gas passes directly from the producers 
to the gas header. 

Other Applications as a Fuel.— The abundance of natural gas and the 
multiplicity of uses to which it has been applied have led to a much greater 
appreciation of the advantages of gaseous fuel, and have helped to empha- 
size the value of the gas producer. During the past few years there has 
been great development in the utilization of producer gas not only for 
power purposes and in the manufacture of iron and steel, but in other 
industries as well. 



PRODUCER GAS AND GAS PRODUCERS 



459 



Among the uses to which producer-gas fuel has been put are anneaHng, 
japanning, enameling, soldering, brazing, galvanizing, drying, evaporat- 
ing, tempering, casehardening, type casting, yarn singeing and heating 
molds, wash kettles, ladles, stoves, bakers' ovens, and cooking. It has 




Fig. 256. — Gas-producer plant for metallurgical purposes. 

also been used quite extensively in brick, lime and cement kilns, and 
in various types of ore-roasting furnaces. 

Fuels Used. — Anthracite. — ^Little difficulty has been experienced in 
handling good grades of anthracite coal in gas producers. Occasionally 
some trouble is experienced due to the character of the ash or to a low 



460 ENGINEERING OF POWER PLANTS 

ash-fusing temperature. In the main, however, this fuel has been found 
very satisfactory. For most sections of the country the price of anthra- 
cite is relatively too high to warrant its use in plants of large capacity. 
It is, therefore, largely utilized in plants not exceeding 500 hp. Little 
has been done in this country with gas producers for the utilization of 
anthracite screenings or material from the culm pile. 

Anthracite coal may be utilized to good advantage in plants of either 
the up-draft or the down-draft type. Inasmuch as it is comparatively 
free from tar, anthracite is commonly used in the up-draft producer of 
the suction type. 

A single installation of 4,000 hp. of down-draft producers is using an- 
thracite at $11.30 per ton in preference to bituminous coal for which the 
plant was designed. Although the company owns bituminous mines, it 
places a value of $8 per ton upon its books for the bituminous coal. On 
this basis of $8 per ton for the bituminous coal and S11.30 per ton for the 
anthracite, a year's operation shows financially in favor of the anthracite. 
Outside of two or three installations, the individual anthracite plants of 
this country do not exceed a few hundred horsepower. 

Bituminous Coal. — Satisfactory gas producers have been designed for 
the use of both bituminous coals and lignites of good quality. There is 
comparatively little difficulty in handling, on a commercial scale, such 
plants provided the fuel is low in ash, has a fairly high ash-fusing tempera- 
ture and does not give serious trouble from caking and clinkering. Un- 
fortunately these restrictions are too exacting to fit usual practice in the 
United States with low-priced fuel. The European situation, where they 
are able to specify quite definitely the characteristics of the coal, is very 
different. 

The answer to a query as to whether producers have been successfully 
designed for the use of bituminous coals and lignites, is ''Yes" for bitu- 
minous coals and lignites of high grades and although it is not ''No" for 
other grades of bituminous coals and lignites, yet it is realized that low- 
grade fuel, high in ash and prone to clinker troubles, is not regarded in 
the majority of cases as worth the time and effort required. Bituminous 
coals and lignites of good grade may be successfully used in the up-draft 
producer if adequate equipment is installed for scrubbing the gas and 
removing the tar and in the down-draft producer of the continuous type 
and in the double-zone producer. 

One of the largest single generators in the United States has 210 sq. 
ft. of fuel bed area burning 2,750 lb. of Illinois bituminous coal per hour. 
There is no apparent reason why single-shell producers of this type should 
not be built four times this capacity. 

Lignite and Peat. — Both lignite and peat have been successfully used 
in various types of producer plants. Many commercial installations are 



PRODUCER GAS AND GAS PRODUCERS 



461 



operating on the former fuel in this country. Peat has not been com- 
mercially developed in the United States, but in Europe it is extensively 
used as a producer gas fuel. 

Amount of Fuel Used by Producer-gas Power Plants in the United 
States.^ — An estimate of the horsepower capacity of gas producers in 
operation for power purposes in the United States in 1915 and the amount 
of fuel used by these plants is: 

Horsepower 
For anthracite coal: 

Plants of more than 500 hp. rating 40,000 hp. 

Plants of less than 500 hp. rating 95,000 hp. 

For bituminous coal 130,000 hp. 

For lignite 15,000 hp. 

A corresponding estimate of the annual fuel consumption of these 
plants is: 

Anthracite 240,000 short tons. 

Bituminous 400,000 short tons. 

Lignite 60,000 short tons. 



• 700,000 short tons. 

Use of Low-grade Fuels. — In the United States the majority of plants 
are using good-grade fuels, but economic conditions will necessitate before 
many years use of so-called low-grade material. 

Although commercial conditions make reliability of operation and 
plant capacity imperative, many plants could today utilize to advantage 
relatively cheap, poor grades of fuel with an assurance of both reliability 
and capacity and a net financial gain. 

The most difficult problem seems to be that of securing thoroughly 
competent men for the careful supervision of such installations. As 
indicated below the Bureau of Mines has demonstrated beyond a doubt 
the possibilities of actually using the following fuels in gas producers. 



Fuel from 



Variety or size 



Per cent. 



Per cent, 
moisture 



Pounds of fuel, as 

fired consumed in, 

producer per b.hp.-hr. 



New Mexico . . 
Tennessee .... 

Iowa 

Wyoming 

Wyoming 

Illinois 

Brazil, S. A. . . 
West Virginia. 
Pennsylvania . 
Pennsylvania . 
West Virginia. 



Run-of-mine 
Run-of-mine 



Run-of-mine 

Bone 

Run-of-mine 

Bone 

Washery refuse 

Washery refuse 

Bone 



19.63 
20.57 
20.70 
20.72 
21.73 
23.12 
23.44 
28.08 
30.35 
31.89 
43.74 



3.62 
3.55 

16.69 
9.44 
8.65 
8.67 

10.96 
2.91 
2.68 
2.25 
0.47 



1.10 
1.45 



56 
70 
83 
88 
02 



1.26 
2.34 
2.76 
1.65 



462 



EmiNEERlNG OF POWER PLANTS 



Pounds of Fuel per Square Foot of Fuel-bed Area per Hour. — One of 

the most important commercial items connected with the design and also 
with the operation of gas producers is the determination of the number of 
pounds of fuel consumed per square foot of fuel-bed area per hour. This 
rate of fuel consumption varies radically with different types of plants 
and with different grades and different types of fuel and has led to much 
difficulty in designing and in rating producers. Early work in this coun- 
try followed European practice almost entirely and thereby occasioned 
a great deal of trouble in properly rating the pioneer plants and brought 
about the ultimate failure of many of them. Under certain European 
conditions, in which fuels of a definite grade are specified, high rates of 
fuel consumption may be obtained. It is not impossible to secure similar 
rates of consumption under corresponding circumstances in this country, 
but as selected fuels are seldom obtainable except under test conditions, 
it has been found that in general in the United States the rate of fuel con- 
sumption per square foot of fuel-bed area does not average much over 
one-half the amount originally guaranteed by early manufacturers. 
This fact has, of course, led to a decided modification in the design and 
proportions of many plants. 

Returns from the operators of plants throughout the United States 
indicate the following rates of fuel consumption per square foot of fuel- 
bed area to be good average commercial practice. 



Anthracite 
coal 



Avg. Max 



Bituminous 
coal 



Avg. Max 



Lignite 



Avg. Max 



Peat 



Avg. 



Wood 



Avg. 



Up-draf t plants : 

(a) Fuel, as fired. 

(6) Fuel, dry 

Down-draft plants: 

(a) Fuel, as fired. 

(6) Fuel, dry 

Double-zone plants: 

(a) Fuel, as fired. 

(6) Fuel, dry 



10.0 
10.0 



14.0 
13.5 



8.5 
8.0 

17.5 
16.5 

13.5 
12.5 



14.0 
13.0 

23.5 
22.0 

18.5 
17.5 



12.0 
8.5 

26.5 
18.5 

21.5 
15.0 



17.0 
12.0 

31.5 
22.0 

27.0 
19.0 



15.0 
12.0 

35.5 
25.5 



14 



Pounds of Fuel per Horsepower per Hour. — Producer-gas investiga- 
tions of the United States Geological Survey and the Bureau of Mines 
conducted with plants not above the average in efficiency showed the 
following approximate fuel consumption per brake horsepower per hour. 



PRODUCER GAS AND GAS PRODUCERS 
Pounds per Brake Horsepower per Hour 



463 





Bituminous cc 


)al 


Lignites 


Peati 




Avg. 


Max. 


Min. 


Avg. 


Max. 


Min. 


avg. 


Fuel as fired . . . 
Fuel, dry..... . 


1.3 
1.2 


2.0 

1.8 


0.8 
0.8 


2.0 
1.63 


2.8 
2.02 


1.5 
1.35 


2.6 

2.0 



Although these figures were secured during the progress of regular 
tests, yet the conditions outlined in reports of the Bureau of Mines indi- 
cate clearly that equally good results should be readily secured in the 
average commercial producer-gas plant. 

A more direct comparison between the results of commercially oper- 
ated plants and those from the Government Station may be had by an 
inspection of the following table. 



Pounds of Fuel as Firee 


> PER 


Brake Horsepower per Hour 






Anthracite coal 


Bituminous coal 


Lignite 


Peati 
avg. 


W00d2 




Avg. 


Max. 


Min. 


Avg. 


Max. 


Min. 


Avg. 


Max. 


Min. 


avg. 


Bureau of Mines. . . 
Commercial plants 


1.3 


1.5 


1.3 


1.3 
1.4 


2.0 

2.4 


0.8 
1.0 


2.0 
2.5 


2.8 
3.0 


1.5 
2.0 


2.6 


3.3 



The relation between the pounds of fuel per brake horsepower-hour 
and the calorific value of the fuel may be seen by referring to the following 
Fig. 242. 









Sl.5 
1.0 
0.5 





Based 


/^T, T7„q1 




w.-^-l 






■n 




Based on Dry Fuel 




■^ 






































■^ 


-^ 


■«.. 


■-, 


.^ 




































;=; 




L 




































— ' 
















■ 














1 







•^ 8000 10000 12000 14000 

B.T.U. p.ej Lb. of Fuel 

Fig. 257. 

Composition of Gas. — The composition of producer gas varies with 
the type of producer, the methods and skill used in operating, the uni- 
formity and regulation of the air and steam supply, the kind and quality 
of fuel used, the depth of fuel bed, the distribution of the fuel and the 
uniformity in size of the fuel. 

The average of several typical analyses of producer gas from the 
1 One sample of peat only. 2 Qne sample only. 



464 



ENGINEERING OF POWER PLANTS 



Bureau of Mines testing plant and the average of the figures presented 
for plants in commercial operation are as follows: 



Up-deaft Plants 





From anthra- From bitumin- 
cite coal ous coal 


From lignite 


From peati 


From woodi 




Bureau 

of 
Mines 


Com- 
mer- 
cial 
plants 


Bureau 

of 
Mines 


Com- 
mer- 
cial 

plants 


Bureau 

of 
Mines 


Com- 
mer- 
cial 

plants 


Bureau 

of 
Mines 


Com- 
mer- 
cial 

plants 


Bureau 

of 
Mines 


Com- 
mer- 
cial 
plants 


Carbon monoxide 
(CO) 




22.7 
0.0 
0.0 

15.5 
5.5 
0.3 

56.0 


18.28 
3.12 
0.18 

12.90 
9.84 
0.04 

55.64 


24.4 
3.7 
0.1 

11.6 
4.8 
0.6 

54.8 


21.00 
2.20 
0.40 

18.50 

12.40 
0.00 

45.50 




21.0 
2.2 
0.4 

18.5 

12.4 
0.0 

45.5 




■ . 


13.6 


Methane (CH4) 








8.0 


Ethylene (C2H4) 








0.0 


Hydroaren (H2) 








4.0 


Carbon dioxide (CO2) 









12.9 


Oxygen (O2) 






0.0 










61.7 



















Down-] 


DRAFT 


Plants 












From anthra- 
cite coal 


From bitumin- 
ous coal 


From lignite 


From peat 


From wood 




Bureau 

of 
Mines 


Com- 
mer- 
cial 
plants 


Bureau 

of 
Mines 


Com- 
mer- 
cial 

plants 


Bureau 

of 
Mines 


Com- 
mer- 
cial 

plants 


Bureau 

of 
Mines 


Com- 
mer- 
cial 
plants 


Bureau 

of 
Mines 


Com- 
mer- 
cial 
plants 


Carbon monoxide 
(CO) 






19.1 
1.1 
0.0 

11.4 
7.6 
0.2 

60.6 


23.6 
1.5 
0.3 

12.4 
4.0 
0.2 

58.0 


15.0 
1.7 
0.0 

13.3 

11.5 
0.2 

58.3 




14.8 
1.5 
0.1 

13.3 

12.9 
0.6 

56.8 








Methane (CH4) 








Ethylene (C2H4) . . 








Hydrogen (H2) 








Carbon dioxide (CO2) 
Oxygen (O2) 














Nitrogen (N2) 

















Oil-gas Plants ^ 

Fuel, crude oil 

Carbon monoxide (CO) 10.2 7.4 

Methane (CH4) .. 6.1 12.7 

Other hydrocarbons (C^Hy) . 3.8 2.6 

Hydrogen sulphide (H2S) 0.0 3.1 

Hydrogen (H2) 10.6 

Carbon dioxide (CO2) 6.1 4.5 1 

Oxygen (O2) 0.0 

Nitrogen (N2) 63.2 69.3 

Heat Value^ of the Gas. — The heat value of the gas from different 
fuels determined from the average of a large number of tests reported 
by the Bureau of Mines and also from the figures submitted by the opera- 
tors of plants in commercial operation are: 

1 One sample only. 2 Reports from two commercial plants. 

3 Higher heat values used entirely in these notes. 



PRODUCER GAS AND GAS PRODUCERS 465 

British Thermal Units per Cubic Foot of Gas 





From anthra- 
cite coal 


From bitumi- 
nous coal 


From lignite 


From peat 


From wood 




AVg. 


Max. 


Avg. 


Max. 


Avg. 


Max. 


Avg. 


Max. 


Avg. 


Max. 




Up-draft Plants 


Bureau of Mines 

Commercial plants. . . 


138 




152 

151 


176 
175 


158 
157 


188 
185 


175« 


.... 


133« 






Down-draft Plants 


Bureau of Mines 

Commercial plants. . . 







110 
.123 


123 
130 


111 


127 


115^ 


119^ 








Double-zone Plants 


Bureau of Mines 
Commercial plants. . . 






id) 




118 













Oil-gas Plants 

Gas from crude oil 
Avg. Max. 

Bureau of Mines 

Commercial plants 215" 230" 

° One sample only. ^ Two samples only. " Two plants only, (d) Tests indi- 
cate this figure to be approximately 115. 

Cubic Feet of Gas per Pound of Fuel. — 

Cubic Feet of Standard (60°F. and 30 in. Hg.) Gas per Pound of Fuel 

Up-draft Plants 





From bituminous coal 


From lignite 


From peat 




As fired 


Dry 


As fired 


Dry 


As fired 


Dry 




Avg. Max. 


Avg. 


Max. 


Avg. 


Max. 


Avg. 


Max. 


Avg. 


Max. 


Avg. 


Max. 


Bureau of Mines 

Commercial plants. . . 


61 

75 


101 
96 


65 


104 


36 


46 


46 


53 


30« 




38" 






Down-draft Plants 


Bureau of Mines 

Commercial plants . . . 


65 

79 


80 

82 


68 


82 


36 


44 


52 


61 


29^ 


3P 


40& 


446 



One sample only. ^ Two samples only. 



466 



ENGINEERING OF POWER PLANTS 



The variations of the gas production with the calorific value of the 
fuel are shown by the following Bureau of Mines data from an up-draft 
pressure plant. 












Based 




■F.ifil 




"ITirorl 






r 


n 


Based on Dry Fuel ^^ 
























^f 
























-^ 


> 




















^ 


^ 


■:z 


-- 






















--1 


^ 




































































































f 






' 


■' 


' 





10000 12000 wooo 

B.X.JJ. per Lb. of Fuel 

Fig. 258. 



On the basis of the average figures from both the Bureau of Mines 
Testing Station and commercial plants, the following gas yield and heat 
value may be expected per ton (2,000 lb.) of fuel as fired. 



Fuel 


Cubic feet of gas per ton 
of fuel as fired 


B.t.u. per 

cubic foot of 

gas 


B.t.u. in gas per ton 
of fuel as fired 




Up-draft Plants 


Charcoal 

Anthracite 

Bituminous coal 


160,000 

140,000 

135,000 

72,000 

60,000 


135 
135 
150 
155 
175 


21,600,000 
18,900,000 
20,200,000 


Lignite 

Peat 


11,100,000 
10,500,000 




Down-draft Plants 


Bituminous coal. 


145,000 
72,000 
60,000 


110 
110 
115 


16,000,000 


Lignite . 


7,900,000 


Peat . . . 


6,900,000 







Cleaning the Gas Generator.— Although in some types of producer 
plants the cleaning out of ashes and clinker is a dirty and tedious job, the 
majority of plants manufactured today are adapted for continuous ash 
removal so that the labor in operation has been materially lessened. 
Aside from plants of the intermittent character, the labor of cleaning 
seems to depend largely upon the man in charge of the plant. 

The variation in the time required for this cleaning, as reported by 
the operators of commercial plants runs from }4 hr. time of one man to 
several hours' time of two or three men. Although some operators have 
serious clinker troubles, the majority are now able to avoid this difficulty. 



PRODUCER GAS AND GAS PRODUCERS 



467 



Time Between Periods of Drawing Fires. — With the exception of 
intermittent producers in which fires must be drawn every few days — 
usually from 6 to 15 days — many plants are now practically continuous 
as shown by the following records of commercial installations. 



Hp. of each gas 


Total hp. of 


Fuel 


Time between periods of drawing 


generator 


plant 




fires 


250 


500 


Anthracite 


Four years. 


300 


300 


Anthracite 


Once a year. 


300 


300 


Anthracite 


Indefinite. 


400 


400 


Anthracite 


Not drawn. 


200 


400 


Bituminous coal 


Once a year. 


370 


1,100 


Bituminous coal 


Not drawn except for repairs. 


650, 1,000 


3,650 


Bituminous coal 


Once a year. 


2,500 


2,500 


Bituminous coal 


Six months to 1 year. 


100 


100 


Lignite 


Four months. 


200 


200 


Lignite 


Two years. 


300 


300 


Lignite 


Once a year. 



Power Required by Producer Auxiliaries. — 

Percentage of Total Plant Power 





Installed as auxiliaries 


Actually used by auxiliaries 




Max. 


Min. 1 Avg. 


Max. 


Min. 


Avg. 


Up-draf t plants 

Down-draft plants 


15.0 
10.0 


0.7 
2.0 


4.3 
5.0 


6.2 
10.0 


0.7 
2.0 


2.8 
3.8 



Standby Fuel. — Many controversies have arisen regarding the 
standby losses in producer-gas plants. Two very different values are 
reported under test and under commercial operating conditions. Several 
writers on the subject are in the habit of allowing per standby producer 
hour from 3 to 6 per cent, of the fuel charged in the producer per operat- 
ing hour. 

An attempt was made to secure commercial figures from several 
plants but the returns are so greatly at variance that no deductions of 
value can be presented. The figures reported show standby percentages 
ranging from 3 to 33. 

Vaporizer Water Required. — Returns from different operators and 
tests vary considerably but average figures seem to be: 



468 ENGINEERING OF POWER PLANTS 

Pounds water per pound fuel fired 
Fuel Up-draft plants Down-draft plants 

Anthracite . 7-1 .0 

Bituminous coal . 7-1 .0 . 23 

Lignite 0.0-0.7 0.0 

Peat (25 to 30 per cent, moisture) 0.0 0.0 

It is possible in some gas power plants to generate the required steam 
by means of boilers heated by the exhaust from the gas engines. Plants 
in service are reported as generating from 2 to 3 lb. of steam per horse- 
power-hour. 

Twelve per cent, or more of the power produced in gas engines is 
available from the waste heat for steam generation. 

In large metallurgical operations the amount of steam required in the 
producer blast averages about 35 or 40 per cent, of the weight of fuel 
gasified. This is approximately 1 hp. of steam per ton of coal gasified 
per 24 hr. 

Scrubber Water Required. — The scrubber water is rated on the basis 
of cubic feet per 1,000 cu. ft. of gas scrubbed. In the up-draft plant this 
includes the water used by the centrifugal tar extractor. 

Average figures are: 

Bureau of Mines tests, 9.7 cu. ft. for up-draft plants. 

Bureau of Mines tests, 10.5 cu. ft. for down-draft plants. 

Commercial plants, 14.2 cu. ft. for average for all types of plants. 

The high figure reported by commercial plants is undoubtedly due to 
the fact that in many of these plants water is practically free. 

Uses of Tar from Producer-gas Plants. — The indications are that 
much more general use is made of the tar from producer-gas plants in 
Europe than in this country. 

In England it is used for road making, roofing, briquetting fuel, patent 
medicines, painting the ends of sawed timber for regulating the drying, 
etc. In many plants it is converted into pitch. 

From 90 to 150 lb. of water-free tar are reported per ton of coal. 

The price received varies from $1.25 to $4.25 per ton. 

A common method of selling in small plants is 50 cts. per barrel. 

One company reports 14.5 lb. of pitch per ton of coal, the tar being 
converted into pitch. 

In the United States a few companies operating producer plants utilize 
the tar as follows: 

(a) Fired under boilers in main boiler plant. One plant reports a 
saving of 5 tons of coal a day, equal to $10. 

(&) Distilled for oil, creosote and pitch. 

(c) Run back into gas producers. 

{d) Mixed with fuel oil for cement burning. 



PRODUCER GAS AND GAS PRODUCERS 



469 



The amount of water-free tar from American fuels seems to run on 
the average 300 lb. per ton of coal and 100 lb. per ton of lignite. 

Mechanically Stirred and Revolving-grate Producers. — Various 
methods of avoiding difficulties from clinke.ring and from channels in pro- 
ducer-gas plants have been employed. Among those which tend to 
do away with hand-poking of the fuel bed are mechanical stirring, rota- 
tion of the fuel bed in sections and revolving eccentric grates. 




Fig. 259. — Mechanically-stoked producer. 

It is claimed by the advocates of these mechanical systems that they 
of necessity produce more uniform conditions in the fuel bed than can 
be secured by hand-stoking due to the fact that they are absolutely 
mechanical and must operate at regular intervals without being subject 
to the whims or indifferences of the operator. It is also claimed that a 
much more uniform condition of the fuel bed is secured due to the con- 



470 



ENGINEERING OF POWER PLANTS 



tinual agitation and grinding down of the ash. The uniform fuel-bed 
conditions claimed naturally tend to produce a more uniform grade of 
gas and ought to result in a relatively large production of gas per square 
foot of fuel-bed area. 

The opponents of this method of procedure claim that all such me- 
chanical devices are absolutely lacking in judgment and consequently 




5^k^w 



Fig. 260.— Revolving eccentric-grate gas producer. 

do their stoking in a manner which is not adapted to the highest efficiency 
and most economic conditions required in plants subjected to varying 
demands. It is also claimed that all such equipment adds materially to 
the care of such a plant and that this apparatus is forever undergoing 
repair and failing to respond to the requirements put upon it. It is also 
claimed that in some of the types of mechanical stokers on the market 
the waste of fuel by way of the ashes is excessive. 



4 



PRODUCER GAS AND GAS PRODUCERS 



471 



Revolving Eccentric-grate Gas Producer. — The demand for a gas 
producer to handle all grades of fuel, especially those grades usually sent 
to the dump, brought to the European market a few years ago the revolv- 
ing eccentric-grate producer. It has recently appeared on the American 
market. This producer appears in several forms, the superiority of 
each form being firmly established in the minds of its advocates. 

The essential features of these producers are shown in Fig. 260. 




Fig. 260a. — Gas producer with floating agitator. 



Among the most important advantages claimed for revolving-grate 
producers as compared with the fixed-grate type is constant and auto- 
matic ash removal instead of ash removal by hand. Dependent upon- 
this primary advantage rest the following claims for the revolving grate : 
(1) Low labor cost for handling ashes; (2) more uniform and more com- 
plete combustion; (3) operation for months without interruption; (4) 
ability to handle much more fuel per square foot of fuel-bed area; (5) 
less space per 1,000 cu, ft. of gas produced or per horsepower of plant; 



472 ENGINEERING OF POWER PLANTS 

(6) freedom from dust and the usual excessively hot and dirty condi- 
tions during removal of ashes; (7) production of a gas of closely uniform 
quality; (8) reduction in the cost of upkeep. 

If, in addition to rotating the grate, the grate be placed slightly off 
center, a feature is introduced that is probably of far greater value in 
handling high-ash clinkering fuels than the mere rotation of the grate. 

The degree of eccentricity may easily be varied to suit the grade of 
fuel handled. For fuels that give no trouble from clinkering, or from 
which the ash is fine, the eccentricity may be reduced to zero, but for 
fuels that give excessive clinkering troubles or from which the ash is coarse 
the eccentric grate is found of value as it tends to grind the ash in such 
a manner as to prevent the clogging of the system. 

The speed at which the grate revolves is determined by the ash con- 
tent of the fuel and the demand upon the producer. The usual rate is 
from 3^^ to lyi, revolutions per hour. The speed of the grate is so slow 
that little power is required to drive it. The figures given by the manu- 
facturers is about 3-^ hp. for a producer of normal size. The usual rac- 
tice, however, is to install motors of 1 to 2 hp. for this purpose. 

Use of Water Jacket. — Experience with European fuels has shown 
that even with the eccentric revolving grate and the usual producer-shell 
construction clinker troubles are not entirely eliminated when a low-grade 
fuel with low ash-fusing temperature is used. A further important 
feature — probably the most important single item — for overcoming clink- 
ering and the tendency of the ash to fuse with the producer lining is 
water jacketing the part of the producer shell surrounding the hot zone. 
This construction is shown in Figs. 245 and 246. 

The extent of this jacketing varies from none for coals that give no 
trouble from clinker formation or tendency to fuse with the producer 
lining to a maximum for those fuels that give such clinkering and fusing 
difficulties. 

In certain designs an additional variation is made in the height of the 
grate to correspond to the clinkering tendency of the fuels used. 

Revolving-grate producers are made of either the dry- or wet-bottom 
type. For extremely fine fuels, such as fine slack and coke breeze, 
requiring relatively high air pressure for successful gasification, the 
dry-bottom ashpit is regarded by some manufacturers as being the more 
desirable on account of the excessive depth of water required by the 
wet-bottom type. 

Advantages of Revolving-grate Producers. — The revolving-grate pro- 
ducers are reported to gasify two to three times as much fuel per square 
foot of fuel-bed area per hour as can be gasified in corresponding up-draft 
pressure producers with fixed grates. In the operation of the plants gas 
leakage is small, as poking of the bed is reduced to a minimum. Work 



PRODUCER GAS AND GAS PRODUCERS 473 

about the producers is thus rendered much more agreeable than is usual 
with up-draft pressure plants. 

Claims of very low percentages of carbon in the ash are also made 
for this type of producer, the reported record for one installation being 
5 per cent, carbon, or 0.47 per cent, of the fuel gasified. 

The claims advanced regarding the steam requirements for clinkering 
coals used in producers with water jackets around the hot zone are to 
the effect that not more than one-quarter as much steam is required as 
in the jacketless type with fixed grate. The figures given for comparison 
are 1 lb. of steam per pound of fuel for the fixed-grate jacketless producer, 
and 0.25 lb. for the revolving eccentric-grate jacketed producer. Results 
with United States coals in fixed-grate jacketless producers indicate that 
1 lb. of steam per pound of coal is rather high for plants of good size. 
Seven-tenths of a pound is nearer the figure, although there are un- 
doubtedly many plants, indifferently operated, that are not below the 
1-lb. rate. 

Efficiency of Gas Producers. — Two efficiencies are usually recognized 
for producer-gas power plants. 

(a) Efficiency of conversion and cleaning. 

(6) Producer-plant efficiency. 

By the first of these is meant the ratio of the actual number of heat 
units in the clean, cold gas delivered to the gas holder or engine to the 
number of heat units in the dry coal actually charged into the producer 
for a given time interval. In determining this efficiency no account is 
taken of the power required to drive any auxiliaries necessary for the 
manufacture of the gas and no allowance is made for any fuel used in 
generating the steam required in the blast in plants in which this steam 
is generated by means of an auxiliary boiler. Under ordinary conditions 
this is the efficiency upon which the manufacturer bases his guarantee 
usually expressing it in some such terms as: ''We guarantee the gas- 
generating system to operate commercially when supplied with fuel ap- 
proved by us and containing not less than .... B.t.u. per pound of dry 
fuel and when handled according to our instructions to deliver in the 
form of gas .... per cent, of the heat units contained in the fuel used 
in the gas generator." 

This efficiency, as defined above, relates primarily to power installa- 
tions in which the gas is used in engines or to other types of plants in which 
the gas is cooled before being utilized. Under furnace conditions and 
other appHcations in which the gas passes directly from the producer to 
the point of utihzation without cleaning or cooling beyond radiation 
losses, the efficiency of conversion is understood to mean the ratio of the 
number of heat units in the hot gas direct from the producer to the num- 
ber of heat units in the dry coal consumed in the producer for any given 



474 



ENGINEERING OF POWER PLANTS 



time interval. This efficiency will usually be considerably higher than 
the corresponding efficiency for the cool, clean gas as the hot gas usually 
carries considerable materials in the nature of tarry vapors and gases 
which add to its heat value but. which in cooling are condensed and are 
carried away in the scrubbing process. 

The second efficiency, or that of the gas-producer plant, is the ratio 
of the B.t.u. in the cold gas delivered to the gas holder or engine to the 
number of heat units equivalent to the total dry coal consumed in the 
producer, the total dry coal required by auxiliary boilers for generating 
steam and any power required for driving auxiliary equipment used in 
the manufacture of the gas (such as centrifugal tar extractors, cleaners, 
etc.). 

The principal heat losses in gas-producer operation which seriously 
affect the efficiency are: (a) heat in the gases leaving the producer; (b) 
radiation losses; (c) heat carried away with the ashes. The first of 
these is the largest, averaging, according to different investigators, 
about 10 per cent, of the total heat value of the gas. The temperature 
of the gas leaving the producer usually runs from 800°F. to 1,200°F. 



100 











































-! Based oji Dry Fuel 






















































































































L-J 


— 




— 


:r= 








r^ 






















~ 


~ 












































. 










, 


... 


_> 






r 1 > 






. 


, 



8000 10000 12000 14000 

B.T.U. per Lb.of Fapl 

Fig. 261. 



Average full-load efficiencies of an up-draft pressure producer operat- 
ing with different grades of fuel are shown in Fig. 261. In general, 
the following efficiencies of conversion and cleaning may be used for pro- 
ducer-gas power plants: 

Up-draft plants, per cent 70 

Down-draft plants, per cent 76 

Double-zone plants, per cent . 73 

For other than normal rating the efficiencies may be taken on the 
following basis: 



Per cent, rated 
capacity 

100 
75 
50 
25 



Per cent, of efficiency 
at full rating 

100 
97 
92 
80 



PRODUCER GAS AND GAS PRODUCERS 



475 



Relative Results from Steam and Producer Gas. — In the ordinary 
manufacturing plant operated by steam power less than 5 per cent, of 
the total energy in the fuel consumed is available for useful work at the 
machine. The same figure holds good for average steam locomotive 
practice. One of the best-designed 'and most skillfully operated plants 
in the United States shows only 1,452 B.t.u. dehvered in the form of 
energy to the busbar from each pound of 14,150 B.t.u. coal supplied to 



-/b" 


\ 










s- 


— <Sr= Steam Plant 






— 






^ 


\ 






P jf^-iToaacer tsras t^ismx 

B.H.P. 
Kw. 










N 




s 












^v. 






















"^ 


\ 




































^ 












^^, 


^^ 










p 






























s 




""^ 


•-- 


"~— ~ 
















--- 


— 


>^ 




s 


p 


— 








" ■ 


--- 







._ 


































. 







■~ 




^ 

^ 




























, 




" 



8000 10000 32000 MXX) 

B.T.U. per Lb.of Fuel as Tired 

Fig. 262. 



the furnace — a thermal efficiency of 10.3 per cent. Probably the maxi- 
mum efficiency obtained with large unit steam turbines, large unit 
boilers and exceptional operating conditions is 14 or 15 per cent. — and 
this but seldom. 

On the other hand, results in gas-power practice may equal the 
following : 

B.t.u. Per cent. 

1. Loss in gas producer and auxiliaries 2,500 20.0 

2. Loss in cooling water in jackets 2,750 22 . 

3. Loss in exhaust gases 4,250 34. 

4. Loss in engine and generator friction 315 2.5 

Totallosses 9^815 78.5 

Converted into electric energy 2,685 21 . 5 

12,500 100.0 

If advantage be taken of the available heat in the cooling water and 
in the exhaust gases, a considerably higher efficiency may be reahzed. 

Comparative tests of small plants (250 hp.) of only fair efficiency 
show the following results for 75 bituminous coals, 6 lignites and 1 peat 
(Florida): 



476 



ENGINEERING OF POWER PLANTS 



Coal Lignite 

Average ratio, fuel as fired per b.hp.-hr. under boiler to 

fuel as fired per b.hp.-hr. in producer 2.7 2.7 

Maximum ratio for above conditions 3.7 2.9 

Minimum ratio for above conditions 1.8 2.2 



Peat 



2.3 



The figures for the producer-gas tests include not only the coal con- 
sumed in the gas generator but also -the coal used in the auxiliary boiler 
for generating the steam necessary for the pressure blast, i.e., the figures 
given include the total coal required by the gas-producer plant. 

Fig. 262 shows the comparative results in graphical form. 

Dimensions of Gas Producers. — An idea of the size of gas producers 
may be had from the following table, showing approximate relations be- 
tween horsepower and fuel-bed area 'for different types of gas generators 
and fuels. 



producer 


Fuel used 


Horsepower per square foot 
of fuel-bed area 


Horsepawer 


Approximate inside 
diameter, inches 


Up-draft 


Anthracite 

and 
bituminous 


8.0 

(Up to about 

500 hp.) 


50 
100 
200 
400 
500 


30 
48 
60 
96 
108 


Up-draft 


Anthracite 

and 
bituminous 


13.0 
(1,000 to 2,500 hp.) 


These sizes, as now 

built, are not circular but made 

up in sections. 


Up-draft 


Lignite 


6.0 


50 
100 
250 


40 

56 
86 


Down-draft 


Bituminous 


13.0 

(Up to about 500 hp.) 

20 or more for 1,000 hp. 

and over 


100 
250 
500 


38 
60 

84 


Double-zone 


Bituminous 


8.5 


100 
250 
500 


46 

74 

104 



Cost of Gas Producers. — The following table gives the approximate 
price of suction, pressure, and down-draft producers from 20 hp. to 2,000. 

The prices are from quotations from various manufacturers. It 
should be remembered that the cost of producer-gas engines is greater 
per rated power than of engines of the same rating for natural or 
artificial gas. 



PRODUCER GAS AND GAS PRODUCERS 



477 



Horse- 
power 



Cost, 
f.o.b., 
dollars 



Cost of 
erection, 
dollars 



Foundation, 
cubic feet 



Cost, 

foundation, 

dollars 



Total cost 
erected, 
dollars 



Cost per 

hp., f.o.b., 

dollars 



Total cost 
per hp., 
dollars 



20 

25 

25 

35 

50 

60 

60 

75 

100 

110 

110 

150 

160 

200 

200 

250 

300 

500 

1,000 

2,000 



650 






800 






1,000 






1,360 




1,100 


150 


1,300 




1,500 






1,650 






1,850 






2,450 






2,500 






3,000 






4,300 


960 


9,500 




18,000 I 


5,100 


23,066 [ 


J,70 






50 



400 



2,140 



15 



120 



150 



555 



927 
1,030 



1,265 

1,900 
3,300 



27,321 



26.00 
22.80 
20.00 

22.70 
18.35 
17.35 
15.00 

12.30 

12.25 
12.50 
12.00 
14.35 
19.00 
18.30 
11.50 



46.27 
42.00 



21.10 

17.30 
20.60 

18.00 
13.66 



Cost of Producer-gas Installations. — Cost per horsepower in dollars. 


Horsepower 


Gas producer and 
engine erected, ex- 
clusive of foundations 


Gas producer and 
engine erected, in- 
cluding foundations 


1 Complete plant 

exclusive of 

buildings 


1 Complete plant 
including 
buildings 


20 


105.00 


108.50 






25 


62.50 
69.50 








60 


74 . 50 




75 


86.50 
62.50 
60.50 








80 






110 


68.00 




110 


62.00 








125 


90.00 
65.00 




100 . 00 
79.00 




250 


68.00 


93.00 


500 












1,000 


55.50 




69.50 


79.50 


2,000 


46.00 


47.50 


56.50 


63.50 


2,800 








76.00 


4,000 








69.00 


4,000 








77.50 


4,800 









72.00 


4,800 









79.50 


5,500 










70.00 


1 T_„l.-J 


« ] : , 


i«„4. ;„ „ _ J. 


1 - _:i- : 


11 X J -;*U 



1 Includes producer, engine, electric generator, and auxiliaries, all erected, with 
suitable foundations. 



478 



ENGINEERING OF POWER PLANTS 
COST OF PRODUCER-GAS 



The Steere Engineering Co. gives the following costs of producer- 
gas for 100 per cent, load factor {i.e., rated capacity 24 hrs. per day, 
365 days per year). 



Cost of one ton 
of coal at plant 


Hot raw producer gas at 
offtake per 1,000 cu. ft., cts. 


Clean cold producer gas 
per 1,000 cu. ft., cts. 


$2.00 


3.13 


4.15 


2.50 


3.55 


4.57 


3.00 


3.96 


4.98 


3.50 


4.38 


5.40 


4.00 


4.79 


5.82 


4.50 


5.21 


6.24 


5.00 


5.63 


6.66 


5.50 


6.05 


7.08 


6.00 


6.46 


7.49 



The company also gives this formula C = 7" + ( 



for estimating the approximate cost of producer-gas for any load factor 
if 

C = cost of producer-gas per 1,000 cu. ft. under conditions specified. 

A = number of feet of gas used per day. 

B = days per week plant is in operation. 

T = cost figures at 100 per cent. L. F. from table. 

R = rated hourly capacity of plant in cubic feet. 

Relative Cost of Steam and Producer-gas Plants. — A careful study of 
the relative cost of the two types of installations leads to the conclusion 
that the complete producer-gas installation for the larger plants — say 
from 4,000 or 5,000 hp. up — costs about the same as a first-class recipro- 
cating engine steam plant of the same size. A 5,500-kw. installation 
cost $73 per horsepower for the producer-gas plant. The bid for the cor- 
responding steam plant was reported to be $74 per horsepower. 

For plants between 1,000 hp. and 5,000 hp. the gas plant will probably 
cost from 10 to 15 per cent, more than the corresponding steam plant, but 
the difference in first cost will be wiped out by the saving in operating 
expenses within about a year. 

For plants below 1,000 hp. the first cost of the producer-gas installa- 
tion is likely to be from 20 to 30 per cent, more than that of the steam 
plant. With coal costing $2.75 per ton it will take about 2 years to make 
up this difference by the saving in operating expenses. 



PRODUCER GAS AND GAS PRODUCERS 



479 



In view of the difficulty of determining the exact basis of comparison 
of the costs of steam and producer-gas plants, the following tables pre- 
pared by Mr. Stott of the Interborough Rapid Transit Co., New York 
City, are presented as indicating the probable relative values of large 
installations, from the standpoint of maintenance and operation. 

A = reciprocating steam engines. 

B = steam turbines. 

C = reciprocating steam engines and steam turbines combined. 

D = producer-gas engine plant. 

E = gas engines and steam turbines combined. 



Operating Costs of Producer-gas Power Plant of the Charlotte (N. C.) 
Electric Railway Co. From Power, Apr. 12, 1910 



B 



Maintenance 

1. Engine room, mechanical 

2. Boiler or producer room 

3. Coal-and ash-handling apparatus 

4. Electric apparatus 

Operation 
Coal- and ash-handling labor . . . 

Removal of ashes 

Dock rental 

Boiler room, labor 

Boiler room, oil, waste. . 

Coal 

Water 

Engine room, labor 

13. Lubrication 

14. Waste, etc 

15. Electrical labor 

Relative cost of maintenance 

and operation 

Relative investment in per 
cent . 



5. 

6. 

7. 

8. 

9. 
10. 
11. 
12. 



2.57 
4.61 
0.58 
1.12 

2.26 
1.06 
0.74 
7.15 
0.17 
61.30 
7.14 
6.71 
1.77 
0.30 
2.52 

100.00 

100.00 



0.51 
4.30 
0.54 
1.12 

2.11 
0.94 
0.74 
6.68 
0.17 
57.30 
0.71 
1.35 
0.35 
0.30 
2.52 

79.64 

82.50 



1.54 
3.52 
0.44 
1.12 

1.74 
0.80 
0.74 
5.46 
0.17 
46.87 
5.46 
4.03 
1.01 
0.30 
2.52 

75.72 

77.00 



2.57 
1.15 
0.29 
1.12 

1.13 
0.53 
0.74 
1.79 
0.17 
26.31 



1.77 
0.30 
2.52 

50.67 

100 . 00 



1.54 
1.95 
0.29 
1.12 

1.13 
0.53 
0.74 
3.03 
0.17 
25.77 
2.14 
4.03 
1.06 
0.30 
2.52 

46.32 

91.20 



The power house contains two main generating units, each a twin- 
tandem double-acting Snow engine of 810 b.hp. and a 540-kw. three- 
phase alternator. The gas producers are the Loomis-Pettibone 
down-draft type for gasifying bituminous coal. The following operating 
records and costs were reported Apr. 1, 1910, at the meeting of the 
American Institute of Electrical Engineers: 



480 ENGINEERING OF POWER PLANTS 

Operating Costs of Producer-gas Power Plant at Works op A. O. Smith Co., 
Milwaukee. From Power, Sept. 20, 1910 

Total engine hours for one year 13,303 

Total kilowatt-hours for one year 3,355,907 

Total pounds of coal for one year. 6,444,281 

Pounds coal per kilowatt-hour 1 . 92 

Average load factor . 45 

Coke used in starting producers 260,292 lb. 

Coke reclaimed 122,371 lb. 

Coke consumed, net 137,921 lb. 

Equivalent in coal, as to cost 192,000 lb. 

6,444,281 lb. 

Total coal for the year 6,636,281 lb. 

Total coal per kilowatt-hour, average . 1 . 98 lb. 

Cost of coal per kilowatt-hour 0,349 ct. 

Cost of power-hour labor per kilowatt-hour 0. 170 ct. 

Cost of producer labor per kilowatt-hour 0. 131 ct. 

Oil for power house . . 065 ct. 

Oil for producer . 005 ct. 

Waste and sundries, power house . 012 ct. 

Waste and sundries, producer house 0.003 ct. 

Repair parts for engines . 046 ct. 

Repair parts for producers . 007 ct. 

Machine-shop work, engines . 016 ct. 

Machine-shop work, producers . 007 ct. 

Excelsior for producers . 003 ct. 

Water, both departments . 071 ct. 

Total cost of power at switchboard per kilowatt-hour . . . 885 ct. 
Power consumed by auxiliaries: 

Cooling water pump, kilowatts per kilowatt-hour 0.0095 

Station lighting, kilowatts per kilowatt-hour 0.0116 

Motor-driven exciter, kilowatts per kilowatt-hour . 0688 

Total kilowatts per kilowatt-hour . 0909 

The generating unit of this plant is an AUis-Chalmers tandem double- 
action gas engine, with 24 by 30-in. cylinders, direct-connected to a 400- 
kw. D.C. generator running at 150 r.p.m. In the producer room are 
two 750-hp. Wood producers. 

Several kinds of fuel have been tried in this installation, the first 
being coke breeze at $1.75 per ton, followed by pea size coke at $2.50 per 
ton. There was found to be a surprisingly large amount of tar in this 
fuel. The large volume of coke which had to be handled was also an 
objection and the fuel finally decided upon was pea anthracite, which 
costs $5.60 per ton delivered. It is stated that 1 ton of the anthracite 
has been found equal to 33-^ tons of the pea coke. 



PRODUCER GAS AND GAS PRODUCERS 



481 



At the time this report was made (September, 1910) the plant had 
been in operation 10 hr. per day for 5 months, and according to numerous 
running tests 1 kw.-hr. is being produced from 1 lb. of pea anthracite 
coal containing 11,500 B.t.u. per pound. 

The total cost of the producer and gas-engine installation was $50,000 
as against a proposed non-condensing steam installation costing $25,000 
for 750 hp., rated capacity of boilers and engines. On this steam plant 
the builders would not guarantee less than 3 lb. of coal per horsepower- 
hour running non-condensing and exhausting to the atmosphere. The 
hot-water heating system, consisting of two locomotive-type boilers and 
40,000 sq. ft. of direct coil radiation, was installed at a cost of $19,000, 
which carries the cost of the entire installation up to $69,000. If the 
non-condensing steam plant had been installed it was estimated that a 
vacuum steam-heating system would have cost $30,000, making the total 
steam installation cost $55,000, or $14,000 less than the present plant 
investment. 

The power plant is now consuming 2,100 lb. of coal for 10 hr. work 
which, at $5.60 a ton, amounts to approximately $5.90 per day, or a 
total of less than $1,950 per annum for fuel. Adding to this, the esti- 
mated consumption by the heating system, during the coldest months of 
the year, of 900 tons of steam coal at $3 a ton, makes a total fuel cost for 
heating and power of $4,650. These figures show a saving of over 60 per 
cent, per annum in fuel over the estimated performance of a steam plant. 
Moreover, it was figured that if a condensing plant had been installed, 
to realize better steam economy, the additional cost of a cooling tower, 
which would have been necessary because the water is bought from the 
city, would have materially increased the investment charges for the 
latter type of plant. 

Operating Costs Reported for Other Commercial Plants. 

The following division of the items making up the cost of operation 
of producer-gas plants is taken from two plants in commercial operation : 



Plant No. 1 


Minimum 


Normal 


Maximum 


Output, kilowatt-hours per day. 


5,000 
0.25 
0.28 
0.17 


8,000 
0.22 
0.17 
0.13 


10,000 
0.20 


Fuel, cents per kilowatt-hour 


Labor, cents per kilowatt-hour 


0.14 


Supplies and repairs, cents per kilowatt-hour. . 


0.11 


Operating cost, cents per kilowatt-hour 

Fixed charges, cents per kilowatt-'iour 


0.70 
0.45 


0.52 
0.28 


0.45 
0.22 


Total cost, cents per kilowatt-hour 


1.15 


0.80 


0.67 



482 



ENGINEERING OF POWER PLANTS 



Plant No. 2 



Per cent, total cost 



Per cent, operating 
cost 



Fuel 
Wag 

Supplies 

Repairs . 

Operating charges 
Fixed charges. . . . 

Total cost . . 



27.4 

29.5 

5.8 

8.6 

71.2 

28.8 



38.4 

41.4 

8.2 

12.0 

100.0 



100.00 =0 .93 cts. per kilowatt- 
hour. = $60 per e.hp.-yr. 



Byproduct Producer-gas Plants. — When producer-gas installations 
are small, not exceeding 3,000 or 4,000 hp., the returns do. not warrant 
any attempt to utilize the constituents contained in the fuel other than 
the gas itself and possibly the tar. In case, however, the plant is to be 
of considerable size, say of 4,000 or 5,000 hp., or more, it is possible to 
not only secure a large supply of producer gas but to separate from 
the fuel certain byproducts which are commercially of considerable 
value. The principal installations for byproduct recovery not only 
produce from bituminous coal large quantities of producer gas but simul- 
taneously with this development yield a liberal quantity of sulphate 
of ammonia. The figures given for some of the best installations in- 
dicate that from each, ton of coal there are produced some 80 or 90 lb. 
of sulphate of ammonia and from 140,000 to 160,000 cu. ft. of gas. 

These plants are of necessity somewhat complicated in their operation 
and are correspondingly high in price so that it is seldom deemed a wise 
commercial venture to install these byproduct plants when the demand for 
gas is small. 

Anthracite coal does not lend itself profitably to this process owing 
to its small percentage of nitrogen, and owing to the high initial price 
of the fuel but the cheaper bituminous coals averaging about 1.3 per 
cent, nitrogen are especially adapted to the successful operation of 
such plants provided they are of sufficient capacity to reduce the oper- 
ating expenses and fixed charges to a reasonable figure per unit of 
output. 

Attention is called to the fact that these byproduct plants are in 
many cases of large proportions; they are not plants of only 2,000 or 
3,000 hp., the majority range from 5,000 to 30,000 hp. One company 
alone reports the installation of byproduct recovery producer-gas plants 
using 3,000 tons of fuel a day and aggregating approximately 300,000 hp. 
The capacity and purpose of a few of the larger installations are as 
follows: 



PRODUCER GAS AND GAS PRODUCERS 



483 




484 



ENGINEERING OF POWER PLANTS 



Capacity and Purpose op Large Producer-gas Plants 



Installa- 
tion No. 


Fuel 
capacity 
per day 


Purpose for which plant was installed 




Tons. 




1 


320 


Special plant for the recovery of byproducts from waste fuels. 
Gas used for firing boilers and for power. 


2 . 


270 


Central distributing station. 


3 


250 


Power and chemical purposes, calcining ore, etc. 


4 


150 


Special plant for the recovery of byproducts. Gas used for firing 
colliery boilers. 


5 


135 


Power, forge, and plate furnaces, fireclay kilns, etc. 


6 


125 


Power and for firing caustic pots. 


7 


120 


Evaporating brine. 


8 


120 


Power and chemical furnaces. 


9 


100 


Firing chrome furnaces. 


10 


100 


Chemical furnaces. 



Character of Plants. — The majority of these plants are used for power 
development and gas heating, and the byproducts, such as sulphate of 
ammonia and tar, are secondary objects in the operation of the plant. 




Fig. 264.^Mond Byproduct Gas Plant, at Dudley Port, South Staffordshire, 

England. 



On the other hand, there are several installations in which power is the 
secondary object, the plant being run primarily for the valuable byprod- 
uct, sulphate of ammonia; which brings a commercial return of $50 to 
$60 a ton. 



PRODUCER GAS AND GAS PRODUCERS 485 

A few plants are operated for the byproducts alone. In certain dis- 
tricts in which the manufacturing and industrial interests do not offer a 
market for the gas, the so-called " byproducts *' become the main products, 
and the true byproduct — producer gas— goes to waste. This condition 
of affairs is peculiarly true in regions in which the local fuel runs high in 
nitrogen. It is reported that an extensive plant of this character is soon 
to be erected in Africa. 

Peat seems to be peculiarly adapted to the requirements for the pro- 
duction of sulphate of ammonia, and several commercial byproduct 
plants using this fuel are now in operation in Europe. Among these are 
two plants in Italy, using 140 tons and 90 tons of peat daily. 

The possibilities of a large installation in connection with extensive 
peat deposits in the United States are now under consideration, consider- 
able preliminary investigation having already been carried forward. 

It is reported that many of the peats of this country contain more than 
2 per cent, nitrogen and in some cases as high as 3 per cent. As calculated 
by Davis in his report on ''Some Commercial Aspects of Peat as a Source 
of Chemical Products," he states that the yield of sulphate of ammonia 
from a short ton of peat containing 2 per cent, nitrogen amounts to 188 
lb. and from a peat containing 3 per cent, nitrogen 282 lb. The market 
price of sulphate of ammonia is approximately $60 per ton which makes 
the above yields worth $5.65 and $8.45 per ton of theoretically dry peat 
gasified. 

Arthur H. Lymn gives ^ the following operating results and estimates 
of working costs : 

i*'Gas Producers with. Byproduct Recovery," Journal of the A.S.M.E., May, 
1915. 



486 



ENGINEERING OF POWER PLANTS 



Table I. 



-Actual Operating Results of Power Gas Plant (Lymn System) 
Driving Large Gas Engines and Firing Furnaces 



First period of 4 weeks 


Total 


Average 

per day of 

24 hr., 

tons 


General average 


Coal consumption of the gas plant 


1,806 tons 

1,889,740 
49,11 tons 

189 . 7 tons 

155 B.t.u. per cu. ft. 

(1,380 cal./cu. m.) 
0.63 gram per cu. m. 
0.04 gram per cu. m. 

J., 967 tons 

1,899,600 
54.3 tons 

231.7 tons 

154 B.t.u. per cu. ft. 
0.38 gram per cu. m. 
0.057 gram per cu. m. 


64.6 

1.76 
6.78 

70 .-2 

1.94 
8.27 


Per kw.-hr. 1.58 lb, 

(0.72 kg.) 
Per hr. 2,812 kw. 


Yield of sulphate of ammonia . . . 


Per ton coal 60 lb 


Yield of tar (containing water) 


(27.1 kg.) 
Per ton coal 230 lb. 




(105 kg.) 


Sulphur contained in the gas (average) 

Tar contained in the gas (average) . 




The auxiliary machines consumed regularly 

71 kw. 
Including 10 per cent, depreciation the gas 

costs per kw.-hr. work out at 0.069 penny. 

Second period of 4 weeks: 


Per kw.-hr, 1,72 lb. 




(0.78 kg.) 
Per hr. 2,830 kw. 


Yield of sulphate of ammonia 


Per ton coal 61 lb. 


Yield of tar (containing water) 


(27.6 kg.) 
Per ton coal 257 lb. 
(117 kg.) 


Sulphur contained in the gas (average) 

Tar contained in the gas (average) . . 




The auxiliary machines consumed regularly 
78 kw 




Including 10 per cent, depreciation the gas 
costs per kw.-hr. work out at 0.07 penny 





Note.— The nitrogen efficiency during these two periods was 70 per cent, 
per cent. 



It is frequently 75 



The working costs of these three plants are based upon the actual 
results in practice referred to above. It has been assumed that the cost 
of labor is 50 per cent, and the cost of apparatus is 25 per cent, more 
in the United States than in England and Germany. 



PRODUCER GAf^ AND GAS PRODUCERS 



487 



Table II. — Estimates op Working Costs for (I) A 2,000-hp. Power-gas Instal- 
lation; (II) A 4,500-KW. Producer-gas Plant, and (III) A Producer-gas 
Plant for Continuous Gasification of 500 Tons op Coal Daily 



Conditions 
Load conditions of plant 



I 
Power 



II 
Power 



III 
Heating 



Hours of full load per annum 

Size of plant in b.hp. or kw. or long tons 
of coal per day 



Cost of coal in dollars per short ton 

Heating value of coal in B.t.u. per lb 

Nitrogen content of coal in per cent 

Cost of sulphuric acid (140° Twaddell) in 

dollars per short ton 

Value of sulphate of ammonia in dollars per 

short ton 

Value of tar in dollars per short ton 

Heat consumption of gas engines in B.t.u. 

per kw.-hr 



4,000 

2,000 b.hp. 
(1,350 kw.) 
2 
12,600 
1.3 

9 

55 

5 

14,900 



8,500 

6,600 b.hp. 
(4,500 kw.) 
1 
12,600 
1.3 



55 
5 

14,300 



8,760 



500 tons 
2 
12,600 
1.3 



55 
5 



Cost of plant 

Producer power gas and ammonia recovery 
plant (Lymn system) in dollars 

Buildings and foundations for same 

Complete gas engine installation consisting 
of gas engines, dynamos, all auxiliary 
machines, exhaust boilers, overhead crane, 
etc., in dollars 



Buildings and foundations in dollars. 



40,600 
4,400 



88,000 



13,000 



126,500 
12,000 



335,500 

(spare set of 

2,250 kw.) 

48,000 



605,000 
55,000 



Total cost of installation. 



138,000 522,000 



660,000 



Working data 

Amount of kw.-hr. per annum 

Tons of coal used (including standby losses) 

per annum 

Tons of sulphate of ammonia recovered per 

annum 

Tons of tar recovered per annum 

Tons of sulphuric acid consumed per 

annum 

Rate of amortization on machines and 

plant in per cent, per annum 

Rate of amortization on buildings and 

foundations in per cent, per annum. . . . 



5,400,000 

4,830 

206 
230 

190 

12 

6 



38,250,000 

29,840 

1,346 
1,500 

1,280 

12 

6 



204,400 

9,210 
10,500 

8,800 

12 

6 



488 



ENGINEERING OF POWER PLANTS 

Table II. — Continued 



Conditions 
Load conditions of plant 


I 

Power 


II 

Power 


III 

Heating 


Annual working costs in dollars of pro- 
ducer gas and ammonia recovery plant 
(Lymn system). 

Cost of coal 


9,660 
5,600 
1,230 
680 
1,710 
5,132 


29,840 

16,630 

3,780 

2,990 

11,520 . 

15,900 


408,800 
49,500 
18,000 
15,330 
79,200 
75,900 


Labor 


Repairs and maintenance.. 


Oil, waste, lighting, etc 


Sulphuric acid 


Depreciation and interest 






Total debit 


24,012 


80,560 


646,730 






Credit by sulphate of ammonia 


11,330 
1,150 


74,030 
7,500 


506,550 
52,500 


Credit by tar 




Total credit .... 


12,480 


81,530 


559 050 






Total annual cost of gas 


11,012 
2.10 


970 
Profit 

0.03 


87,680 
0.32 


Cost of gas in cents per 1,000 cu. ft. (heat- 
ing value 150 B.t.u. per cu. ft. m.) 


Annual working costs of gas-engine plant. 
(Based upon first-class German gas-engine 

practice) 
Cost: Cost of gas as above. . 


Dollars per 
annum 
11,012 

1,250 

840 

3,590 

10,380 


Dollars per 

annum 

970 

Profit 

5,170 

4,420 

10,370 

3,180 




Repairs ... 




Oil, waste, water. 




Labor at American rates 




Depreciation and interest .... 








Total costs 


27,072 


62,170 








Total cost of power in cents per kw.-hr . , . 
Total cost of power in dollars per kw.-yr . . 
Total cost of power in dollars per hp.-yr.. . 


0.50 


0.16 
13.80 
10.30 





Slagging Gas Producers.^ — Many attempts have been made to de- 
velop a gas producer along blast-furnace lines in which the ash should be 
fused and drawn away as a molten mass. 

Little of commercial value has been accomplished along this line in 
the United States, but several such plants are operating with more or less 
success in Europe. Such a plant in Deutsch-Luxemburg inspected by 

* For detailed descriptions, see Bureau of Mines Technical Paper No. 20. 



PRODUCER GAS AND GAS PRODUCERS 



489 



one of the authors in 1914 consisted of four slagging producers approxi- 
mately 10 ft. in internal diameter and gasifying 60 tons of fuel each per 
24-hr. day. The following details are of interest: 

Charge, — Thirty kilos of blast-furnace slag to 1 cu. meter of coke 
breeze. 

Blast. — Preheated. Preheated blast has proved much more efficient 
than cold blast, so additional preheaters are being installed. 

Slag. — The slag from the producers is used for brickmaking. 

Iron. — ^Four hundred kilos of iron are recovered as a daily byproduct 
from 60 tons of fuel. 

Byproduct Coke-oven Gas Plants. — Another gas that has been used 
more or less extensively and successfully abroad and in one or two in- 



Apparatus for Recovery 
of By -Products 




Fig. 265. — Diagram showing utilization of coke-oven waste gases. 



stallations in this country is the gas from the byproduct coke-oven plant 
so that the byproduct coke oven in a sense may be regarded as a gas 
producer. This method of gas generation has attracted considerable 
attention of late and in the minds of some is to become so important that 
the erection of large byproduct coke-oven plants will go on extensively. 
It is claimed that by this process sufficient coke can be secured for prac- 
tically all domestic requirements and that coke thus sold will pay the 
operating cost of the installation and that the gas may be regarded as an 
extra or byproduct. Others claim that the gas is becoming so important 
that it will pay to erect such plants for the value of the gas and that the 
coke will be the extra or byproduct, the gas paying for the cost of operat- 
ing the entire installation. In other words, the opinions seem to be that 
either will pay the operating expense of the plant and the other is the 
profit making byproduct. 



490 



ENGINEERING OF POWER PLANTS 



By-i'koduct Yields from Coal such as jnow Used to Make Fikst-class By- 
product Coke in the Middle States District^ 



To make 1 ton furnace coke, 1.4 
to 1.5 tons coal are required. 

By beehive coking, the by-prod- 
ucts wasted have a heat vahie 
equivalent to G25 lb. of coal. 



Surplus gas. 9,000 cu. ft., 550 B.t.u. 
Used as fuel. 

Tar. 12 gal. Used to make creo- 
sote oil, pitch, lampblack, various 
oils and dye materials. 

Ammonium sulphate. 33 lb. (or, in 
form of 25 per cent, ammonia 
liquor 33 lb.). Used for fertilizer, 
for refrigeration, and for nitric 
acid and other chemical manu- 
factures. 

Benzols (as light oil). 4.5 gal. 
Used for motor fuel, dye-material 
base, phenol and other chemical 
manufacture, solvent and cleanser. 

Coke breeze. 120 lb. Used as 
fuel. 



Fuel value 
equivalent, 
lb. of coal 

350 



133 



(No fuel 
equivalent) 



42 



100 



Total. 625 

Add coal equivalent wasted in beehive oven 200 



Total economy of by-product oven per ton coke 825 

Gas Distribution. — One of the special advantages of gas, both as fuel 
and for power generation in a gas engine, is the ease with which it may 
be piped to different portions of the plant. If the gas is properly cleaned 
and freed from tar it ought to cause no trouble in the distributing lines. 
For such local distribution the pressure can be very low, usually about 
5 lb. per square inch for long-distance transmission, thus making the 
upkeep of the pipe system small and leaks can easily be cared for. There 
is nothing to condense in the pipe lines so no care is required in the way 
of insulation. 

The situation is totally different in the case of steam distribution. 
Here the pressures are high (100 to 150 lb. per square inch). The repair 
bill is often excessive and leaks are a constant source of trouble. Insu- 
lation is required and adds to the cost and the methods of pipe laying are 

1 Abstract of paper presented at a joint meeting of The Franklin Institute and the 
Philadelphia Section of The American Society of Mechanical Engineers, February 
1, 1917. "By-product Coke and Coking Operations," by C. J. Ramsburg and F. W. 
Sperr, Jr. 



PRODUCER GAS AND GAS PRODUCERS 491 

necessarily expensive. Serious losses result from condensation in case the 
steam lines are long and improperly insulated. The pressure in the lines 
must always be high as the steam must enter the engine cylinder at or a 
little above the initial pressure required in the cylinder. For a gas engine 
the only pressure required in the line is enough to insure the delivery of 
the gas, and in many cases the gas is drawn into the engine by the suction 
stroke and is at a pressure below that of the atmosphere. 

Troubles from condensation and leakage and the cost of installation 
usually force the erecting of a large steam engine close to the boilers in 
order to limit these difficulties. With the ease of gas distribution indi- 
cated the gas engines may readily be located at various portions of the 
works. 

The distribution of producer gas over extended areas is destined to 
become a considerable enterprise. 

The Blast Furnace as a Gas Producer. — One of the most common 
types of gas producers is the blast furnace. It is, of course, not built 
primarily for gas production and the gas is a byproduct of the iron manu- 
facture. Its composition is approximately: 

Per cent. 

Carbon monoxide 23 

Carbon dioxide 12 

Hydrogen 2 

Methane 2 

Water vapor 3 

Nitrogen 58 

100 
Calorific value, 85 to 95 B.t.u. per cubic foot. 

As delivered by the furnaces, the gas contains from 3 to 10 grains of 
dust per cubic foot of dry gas. For engine use the dust content must not 
exceed 0.02 grain per cubic foot. 

Blast furnace gas is usually cleaned in three stages: 

1. Dry cleaning to 1.5 to 2 grains per cubic foot. 

2. Static washing to about 0.15 grain per cubic foot. 

3. Mechanical washing (usually by Theisen washers) to 0.015 or less 
grains per cubic foot. 

The Theisen. washer according to Sampson^ requires about 3 per cent, 
of the output of the blast-furnace gas output and 16 to 18 gal. of water 
per 1,000 cu. ft. of gas cleaned. The static scrubbers require 75 to 80 
gal. per 1,000 cu. ft. of gas cleaned, making the total 90 to 100 gal. 

It is claimed that new processes of gas cleaning require only 20 gal. 
of water per 1,000 cu. ft. of gas. 

Mr. H. J. Freyn presents the following calculations which show the 
amount of gas available for power generation in blast-furnace plant 

1 "Practical Operation of Gas Engines Using Blast-furnace Gas as Fuel," C. S. 
Sampson, Transactions A.S.M.E., vol. 35, p. 151. 



492 



ENGINEERING OF POWER PLANTS 



practice. Mr. Freyn's figures are based on a plant of eight furnaces of 
about 450 tons capacity each, producing about 3,600 tons of pig iron per 
24 hr. The amount of blast-furnace gas generated in this plant will be 
22,500,000 cu. ft. per hour, since it is generally agreed that 150,000 cu. ft. 
of gas are liberated per ton of pig iron produced per 24 hr. This gas will 
have an average heat value of 95 B.t.u, per cubic foot. Of this total quan- 
tity, about 40 per cent, or 9,000,000 cu, ft. is used for heating the blast in 
the stoves or lost by leakage. 

For gas-blowing engines, about 2,600 brake horsepower per furnace 
are required, which consume, at the rate of 12,000 B.t.u. per brak^ 



10 Tons of Coke per Sonr 



Evaporation 5% 



Reduction-24 %l 






0SBS^EEMllSEm^ 



\777W/A 




a 
w 

Air Supply 



S^^ 



Gas Engines 

2500 B.H.P. 



■NVsSSxW^VWVVsWW^ 



X\NX\\\\\\\VVNSNSNS> 



-•^^:5^^55^^^^^^^^^^^:^5^^^:^ :^^\N^^^^\\\\\^^^\\\\\\^\V ^^^^<:^^\\^^^^^^^^ 



Luss-14 5 
Heat Consumption in Blast Furnace 52 % 

Fig. 266. — Diagram showing utilization of blast-furnace waste gases. 



horsepower-hour, about 330,000 cu. ft. of gas per hour, or for eight blast 
furnaces 2,640,000 cu. ft. An additional quantity of 460,000 cu. ft. per 
hour for eight blast furnaces will be necessary to produce in gas-electric 
engines the required power to operate the furnace auxiliaries, such as air 
compressors for mud guns, skip hoists, ore-handling machinery, trans- 
fer cars, bells, lighting, and so on. 

The total quantity of blast-furnace gas which has to be deducted 
amounts thus to 12,000,000 cu. ft. per hour. In other words, there will 
remain for use, outside of blast-furnace operation, 10,400,000 cu. ft. per 
hour. This quantity of gas represents at a heat value of 95 B.t.u. per 
cubic foot the total amount of heat of 1,000,000,000 B.t.u. per hour. 

To make use of this available quantity of heat for power generation, 
gas-electric engines or steam turbo-generators can be installed. In the 



PRODUCER GAS AND GAS PRODUCERS 



493 



former case, the available quantity of heat will produce at the rate of 
16,200 B.t.u. per kilowatt-hour at the switchboard, corresponding to an 
average thermal efficiency of 21 per cent., a total of about 60,000 kw. 
(90,000 b.hp.). 

If this available quantity of heat is converted into power through 
gas-fired boilers and steam turbo-generators, the maximum capacity of 
the power plant would be about 30,000 kw. (45,000 b.hp.) if a heat con- 
sumption of 32,500 B.t.u. per kilowatt-hour, or a thermal efficiency of 
10.5 per cent, of the steam plant is assumed. 

Cost of Blast-furnace Gas Electric Power Plants. — The cost of these 
installations apparently runs from about $80 to $105 per kilowatt of 
maximum continuous rating. 

The reported cost of five such installations is: 



Power plant No 

No. of units 

Cap. kw., max. con. rating. . . . 
Cap. b.hp,, max. con. rating.... 
Cost of installation per kw., 

max. con. rating 

(o) Buildings 

(6) Eng. equipment 

(c) Gas cleaning plant 

Grand total, power, plant, 
complete, per kw , . . 



1 

17 
40,000 
56,400 



$9.87 

71.78 

5.85 



$87.50 



% 

11.3 1 

82.0/ 

6.7 



100.0 



2 

2 
4,500 
6,400 



$75,50 
16.80 



$92.30 



% 
81.8 
18.2 



100.0 



3 

4 

9,000 

12,800 



$10.17 

72.75 
14.40 



$97.32 



% 
10. ( 
74. ( 
14.^ 



100.0 



4 

4 

9,000 

12.800 



$10.90 
77.78 
13.00 



101.68 



10.8 
76.4 
12.8 



100.0 



5 

5 
11,400 
16,300 



$10.52 
80.32 
12.76 



% 
10.3 
77.3 
12.4 



103.60 100.0 



One large installation of this character is reported to have a cost a 
little more than $75 per kilowatt. 

Cost of Blast-furnace Gas-electric Power. — The cost of producing 
electric power by means of blast-furnace gas engines in one of the large 
steel plants is reported to be as follows: 



494 



ENGINEERING OF POWER PLANTS 



Cost of Producing Electric Power. All Cost Figures in Cents 
PER Kilowatt-hour 





1910 


1911 


1912 


Capacity in kw 


40,( 
116,535,( 
33.3 

$88.00 
0.0678 
0.0366 
0.0116 
0.0074 
0.0064 


)00 
)00 

% 
17 



25 

42 

58 


40,000 
157,742,510 
45.0 

$88.00 
0.0421 
0.0305 
0.0100 
0.0057 
0.0153 


% 
17 

28 

45 
55 


50,000 


Kw.-hr. produced 


286,575,000 


Use factor, per cent 


64.5 


Cost of installation. 
Per kw 


$88.00 


Labor 


0.0302 


Repairs and maintenance . . . 
Lubricants 


0.0273 
0.0085 


Water 


0.0036 


Miscellaneous 


0.0128 












Total net op. exps 


0.1298 


0.1036 
0.1508 
0.0219 




0.0824 
0.1464 
0.0144 


% 
17.5 


Value of gas . . 




Cost of purification 






Total cost of purified gas 


0.1951 


0.1727 


0.1608 


34.0 


Operating cost without fixed 
charges 


0.3249 
. 4520 


0.2763 
0.3360 


0.2432 
0.2310 


51.5 


Fixed charges at 15 per cent. . 


48.5 


Grand total at switchboard.... 


0.7769 


100 


0.6123 


100 


0.4742 


100.0 



PROBLEMS 

95. With Pennsylvania bituminous coal, what would be the internal diameter of 
a single-generator up-draft producer to supply gas for an engine of 500 hp.? 

96. (a) With a high-grade West Virginia coal, what would be the internal diame- 

ter of a single-generator up-draft producer to supply gas for an engine 
developing 500 hp. when running at normal full load? 
(6) If the engine were developing only 250 hp., how many pounds of fuel would 
be burned per square foot of fuel-bed area per hour? 

97. A lignite mine is estimated to contain 1,000,000 tons of lignite as mined. 
How many gas-producer installations of 2,500 hp. each can this mine supply 
on the basis of a 12-hr. day and full load for 308 days per year for a period 
of 50 years? What would be the fuel-bed area of: 

(a) Up-draft producers. 
(6) Down-draft producers, 
(c) Double-zone producers. 

98. (a) Given a 300-hp. producer-gas engine running at 80 per cent, of rated full 

load; a 100-hp. engine running at 50 per cent, of rated load; an 80-hp. 
engine running at .60 per cent, rated load. Determine the diameter 
of one up-draft pressure producer to supply gas for the plant based on 
average figures allowing for a demand on the producer of 30 per cent, 
above that indicated by the above loading. Coal, bituminous 12,800 
B.t.u, as fired. 



PRODUCER GAS AND GAS PRODUCERS 495 

(6) If a two-generator down-draft unit be installed instead of the up-draft 
unit, what would be the internal diameter of each generator? 

(c) What would be the maifi fuel-bed area for a double-zone producer for the 
same purpose. 
99. Determine the amount of water required by the entire plant, engines and 

producers, of problem 82. 

100. Some of the features of a contract for an up-draft pressure gas-producer in- 
stallation for developing full load with a 750-b.hp. engine are: with bituminous 
coal of 13,500 B.t.u. per pound, not exceeding 10 per cent, ash, the engine 
will not require above 60,000 cu. ft. of gas per hour; the engine is to run on 
the basis of 1 1,000 B.t.u. per brake horsepower per hour at full load ; the internal 
diameter of the producer is to be 11 ft. 

(a) Can the coal indicated be used in the type of producer specified? If so, 

what becomes of the tar? If not, why not? 
(h) Is the fuel-bed area large enough? 

(c) Is the guarantee for number of cubic feet of gas a safe one? 

(d) If a two-generator down-draft unit be installed instead of the up-draft 
unit, what would be the internal diameter of each generator? 

(e) If a steam plant is put in instead of the proposed gas plant, how much 
will the cost of coal for the steam plant exceed that for the gas plant per 
month of 25 days, 10 hr. per day neglecting standby losses, if the coal costs 
$2 per ton (2,000 lb.). 

101. An up-draft pressure producer designed to furnish gas from a 13,500 B.t.u. 
bituminous coal to a 350-hp. engine was recently installed. The price of coal 
has increased and the purchaser is considering the use of lignite or peat in 
place of coal. 

What engine capacity could be maintained with these fuels? 

102. What would be the probable total difference in cost of bituminous coal at 
$2.75 per short ton for developing 350 b.hp. for an 11-hr. day, 308 days per 
year: (including standby losses for 365 days — 308 working days and 57 Sundays 
and holidays), in a pressure gas-producer plant and a steam plant consisting 
of water-tube boilers and a compound-condensing, high-speed engine using 
coal averaging 13,500 B.t.u. as fired? 



CHAPTER XXIII 

COMPARATIVE EFFICIENCIES AND OPERATING COSTS FOR 
DIFFERENT TYPES OF INSTALLATIONS 

RELIABILITY AND CONSERVATION 

In a discussion^ of ''Industrial Power Problems" W. F. Uhl reaches 
the following conclusions. 

Reliability of power supply is of much greater importance to the 
average industry than the cost of power. If the cost of power were 
doubled, it would be hardly noticed on the balance sheet of many in- 
dustries, but shutdowns and speed drop or variation of speed may make 
a decided difference. 

Cost and reliability being nearly equal, it would ordinarily be policy 
to purchase power where available. If the central plant from which 
the power is purchased is relatively large and has a fair load factor, this 
would tend toward fuel conservation. 

Where an industry requires considerable heat for manufacturing 
and heating purposes, power can generally be made cheaper than it 
can be purchased, and fuel would also be saved by making rather than 
purchasing power in such a case. 

Water power owned by an industry in many cases bears the same 
relation to it as does purchased power. If it is located at the industry 
it is often a form of reliability insurance to maintain a water power, even 
if there is no apparent saving due to its use. 

Water powers that save coal should be maintained in any case, and 
there is a splendid opportunity to save fuel by re-development of in- 
efficient water powers. 

There exists a field for fuel conservation and financial gain for both 
central plant and industry, in the possibility of isolated-plant operation 
by the former. 

In the case of water powers owned by industries running only eight 
to nine hours a day, the saving is of decided importance. 

Under certain conditions the saving which would result from central- 
plant operation of isolated steam plants is also considerable. 

SAVING COAL IN STEAM POWER PLANTS 2 

Isolated Plant Versus Central Station Power 

A. If the available power purchased or privately generated is ob- 
tained purely irom a hydroelectric service its use will, of course, save 

1 Mechanical Engineering (A.S.M.E.), November, 1918. 

2 Bureau of Mines Technical Paper 317. 

496 



EFFICIENCIES AND OPERATING COSTS 497 

fuel over any steam-power proposition. If, however, in a steam plant 
all the exhaust steam were sufficiently utiHzed the boilers would still 
have to be operated at about 90 per cent.^ of their former output to 
supply the heating steam (even if at low pressure) if the engines were 
shut down, and the saving in coal would be only 10 per cent, instead 
of 100 per cent. 

B. If the purchased power is produced in a central steam plant 
capable of dehvering a kilowatt hour for, say, 23^^ lb. of coal, then its use 
will waste or save in comparison with a private steam plant, as follows: 

B-1. If all the exhaust steam from any design of private plant 
is absorbed by heating and process work, no central power station^ 
of condensing operation can ever be designed to compete with it in 
the matter of coal consumption. 

If the engines in this private plant were all removed it would still 
require 90 per cent, as much coal as formerly to make low-pressure 
steam for heating, and outside current at 23-^ lb. per kilowatt horn- 
would still have to be purchased. 

If the private plant had been using 8 lb. of coal per kilowatt hour 
it would save eight-tenths of a pound of coal to replace which it would 
buy current costing 23^-2 lb. Thus, for each pound saved in the private 
plant S}i lb. are burned in the central station. This example repre- 
sents the extreme case in favor of the private plant. 

B-2. If the same private plant operating noncondensing wastes all 
of its exhaust steam, coal will be wasted in the ratio of 8 to 2J^ per 
kilowatt used. Coal will be saved by substituting purchased power. 
This example represents the extreme case in favor of the central station 
current, and the ratio is 8 to 23-^ or 3.2 to 1. 

To sum up cases B-1 and B-2, the use of exhaust steam is the deter- 
mining factor. Where it is all used the small private plant generates 
its energy as a by-product of its heating. The engine or turbine acts 
as a pressure reducing valve between the boiler and the heating system, 
and abstracts a small percentage (3 to 12 per cent.) of heat from the 
steam. Therefore shutting down the engine will save only this small 
fraction of the total coal. For most cases of this kind it is safe to say the 
engine absorbs less than 10 per cent, of the heat or fuel. As a matter of 

^ Exhaust steam contains, within a few per cent., as much heat as direct steam. 
Thus an engine or turbine with steam consumptions of 20 lb. and 60 lb. per indi- 
cated horsepower hour will discharge in the exhaust about 88 to 96 per cent, of the 
heat of the steam admitted at the throttles respectively. In the examples given 90 
per cent, is assumed. 

^ Operating condensing in accordance with standard practice. If a central plant 
were designed to furnish exhaust steam to its customers it could then compete on a 
coal basis with the private plant. This is the sound theory of the "city block" or 
''district" system of power and heating. 



498 ENGINEERING OF POWER PLANTS 

fact, many cases could be quoted where no saving of coal occurs when 
the engines are shut down.^ 

Hence for purposes of approximate calculation the power is a pure 
by-product of the heating. But assuming 10 per cent, of the heat of 
the steam to be taken by the engine, then only 10 per cent, of the coal 
consumption will be saved if the heating is done by direct steam. Eight 
pounds of coal per kilowatt hour, the figure assumed, is based upon an 
extravagantly wasteful boiler plant, but even under these conditions the 
small private plant using all its exhaust would save coal over central 
station current for power in a ratio of 33^^ to 1. 

If on the other hand no exhaust steam is used in the same private 
plant, the saving in favor of the central station power is in the ratio 
of the coal used per kilowatt hour for the two cases, or with the figures 
assumed, 8 to 23-^, that is 3.2 to 1. 

It is evident that in a noncondensing private plant, as the use for 
exhaust steam decreases a certain point will be reached where the same 
coal consumption would obtain by the generation of power by either 
type of plant. A still further reduction in the u-tilization of exhaust 
would then throw the balance in favor of central station power. 

This critical point of equal total coal consumption depends upon 
the coal consumed per kilowatt hour in the private plant and the central 
plant, respectively. Thus if the central station has a coal rate of 3 lb. 
per kilowatt hour and the private plant 6 lb., the critical point is reached 
when 1 minus % = }'2 of the exhaust or coal is needed for^ heating, 
and the same total coal will be consumed whether the power is purchased 
or the engine operated. If less than one-half of the exhaust is used, 
the purchased current will effect a saving; if more than one-haK of the 
exhaust is used, running the engine in the private plant will save coal. 

Take another case and assume that current can be supplied at the 
purchaser's switchboard for 2 lb. of coal, and that the small plant pro- 
duces it for 5 lb. Then, if 1 minus % = % of the coal or exhaust is 
needed for heating no change in total coal consumption will occur if 
current is purchased, the engines shut down and boilers operated for 
heating only.^ 

^ There are sound technical explanations for these cases, but it is aside from present 
purposes to enter a detailed discussion. 

2 The proportion of exhaust required for heating represents almost the same 
proportion of coal which will have to be burned for direct steam heating if the engine 
is replaced by purchased power. 

^ Equal coal consumption obtains when the proportion of total coal required for 
heating alone equals one minus the fraction obtained by the ratio of the kilowatt 
hour coal consumptions of the isolated plant to the central plant figured from the 
purchaser's switchboard. Example: With purchased current at 4 fb. of coal and 
private power at 7 lb., an equal coal consumption with either system will obtain 
when the proportion of coal required for heating is 1 minus f^j = ^^ of the total coal. 



EFFICIENCIES AND OPERATING COSTS 499 

If the coal per kilowatt hour for outside current is less than the 
same figure for the private plant, the most coal will be conserved by 
carrying just enough load to furnish exhaust for the heating and buying 
the surplus power. Thus the small plant obtains a part of its power 
as a by-product of its heating and buys the balance for the least total 
coal consumption. This method saves more coal than shutting down 
the small plant entirely, even when a saving would be thus effected. 
There are many cases where at night or during nonheating months 
where an important coal saving can be made by buying the power which 
is in excess of that required to furnish exhaust for heating. 

Still another situation is met when the private plant is of modern 
design and operates solely for generation of power. Such cases would 
be determined purely on a comparison of the coal consumed per kilowatt 
hour. Central station power is produced at consumers' switchboard 
from a minimum of about 1% lb. of coal in the largest and most modern 
plants up to 3 lb., 4 lb., 5 lb., and upward in less efficient stations. 

In moderately large private plants of good design a kilowatt hour 
is produced for a little over 2 lb., while less efficient and smaller plants 
consume up to 10 lb. and over. . In this whole problem it is necessary 
to regard coal as the basis of economy and not money as heretofore. 
Central station interests and private consumers should patriotically 
endeavor to meet each other half way in sacrificing by reduced rates or 
increased expense when important economies in coal are at stake. 

Thermal Efficiencies of Different Types of Engines. — 

1. ^M Ericcson Hot Air Engine. 

2. ^^M Direct-acting Steam Pump. 

3. ^^^^HH Simple Automatic, Non-condensing. 

4. ■■■■■■ Simple Corliss, Non-condensing. 

5. IHI^^^^^II Compound Automatic, Non-condensing. 

6. ■^^^■■■■B Simple Automatic, Condensing. 

7. i^^HHHi^^^H Simple Corliss, Condensing. 

8. ■■■■■■■■^■i Compound Automatic, Condensing. 

9. ■■■■■■■■^■■■■i Steam Turbine, pres. and vac. high. 

10. ■■■^^■^^^■^■H Compound Corliss, Condensing. 

11. ■■■^■■■^^^■■■IH Compound Pumping Engine, Condensing. 

12. ■■■■■■■■■^^^^^^I Compound, Moderate Superheat. 

13. ■■^^^^■■■■■■^^■■i Compound, High Superheat. 

14. ■■■■■^■■■■^■^■■^^■l Triple Expansion Pumping Engine. 

15. HHI^HHHHHBBHBHMHiHI Steam Turbine, pres., vac. and superheat high. 

16. ■■^^^^^^^^■■■■^^^■■■i Quadruple Expansion Pumping Engine. 

17. {^■■■■■i^^lBHBBHBHHBHIHi^^^HHIili^ Gas Engine. 

The graphic chart above shows the relative thermal efficiencies of 
the different engines mentioned as reported by good authorities. The 
thermal efficiencies are based on the indicated horsepower and are the 
maximum officially recorded. 



500 



ENGINEERING OF POWER PLANTS 






Lost in Smoke 
24.6 % 





Fig. 267. — Heat distribution — steam plant. 



Lost in 

Badiation 

and 

Cooling 

18.6^ 



=r=c 



^^i^J^^^^'^wiliAXVVAVW/AVVVAVV^VV^^ 





Fig. 268. — Heat distribution — producer-gas plant. 



Distribution of Heat 
Original heat in the coal = 13,500 heat units per pound 





Steam plant 


Gas plant 


Heat lost in ashes 


2 . per cent. 
4.6 
24.6 

31 . 2 per cent. 
3 . 3 per cent. 

53.5 

7.3 

95 . 3 per cent. 
4.7 per cent. 


1 . 1 per cent. 
18.6 


Heat lost in radiation and cooling 


Heat lost in smoke 




Total losses in boiler and producer 


19.7 per cent. 
4.3 per cent. 

28.5 


Heat lost in radiation and friction 


Heat lost in exhaust 


Heat lost in jacket water ; 


33.5 


Heat lost in auxiliaries. . . 




Total heat losses in entire plant 


86 . per cent= 
14 . per cent. 


Net efficiency of plant 





Relative Cost of Fuel with Different Types of Installations. — The 

following table is, of course, only approximate but it represents average 
practice, and not the best test results. 



EFFICIENCIES AND OPERATING COSTS 



501 



Type of plant and fuel 



Fuel per 

b.hp.-hr., 

pounds 



B.t.u. in 
fuel per 
b.hp.-hr. 



Therm. 

effi., 
per cent. 



Price of 

fuel per 

ton, dollars 



Fuel cost, b.hp. 



Hour, 
cents 



Year,i 
dollars 



I 



Small steam plant 

Anthracite coal 

Anthracite coal 

Anthracite coal 

Anthracite coal 

Bituminous coal ". . 

Bituminous coal 

Bituminous coal 

Bituminous coal 

Large steam plant 

Anthracite coal 

Anthracite coal 

Bituminous coal 

Bituminous coal 

Bituminous coal 

Bituminous coal 

Small producer-gas plant 

Charcoal 

Charcoal 

Charcoal 

Charcoal 

Anthracite coal 

Anthracite coal 

Anthracite coal 

Anthracite coal 

Coke 

Coke 

Bituminous coal 

Bituminous coal 

Bituminous coal 

Bituminous coal 

Large producer-gas plant 

Bituminous coal 

Bituminous coal 

Bituminous coal 

Bituminous coal 

Bituminous coal 

Bituminous coal 



4.00 
4.00 
7.00 
7.00 
4.00 
4.00 
7.00 
7.00 

2.00 
2.00 
1.30 
1.30 
2.00 
2.00 

1.00 
1.00 
1.50 
1.50 
1.25 
2.00 
1.25 
2.00 
1.50 
1.50 
1.25 
1.25 
2.00 
2.00 

0.80 
1.00 
1.00 
1.50 
1.50 
2.00 



56,000 
56,000 
98,000 
98,000 
52,000 
52,000 
91,000 
91,000 

25,000 
25,000 
17,000 
17,000 
26,000 
26,000 

12,000 
12,000 
18,000 
18,000 
15,500 
25,000 
15,000 
25,000 
16,500 
16,500 
16,500 
16,500 
26,000 
26,000 

11,600 
13,000 
13,000 
19,500 
19,500 
21,000 



4.5 
4.5 
2.6 
2.6 
4.9 
4.9 
2.8 
2.8 

10.2 
10.2 
15.0 
15.0 
9.8 
9.8 

21.2 
21.2 
14.1 
14.1 
16.4 
10.2 
17.0 
10.2 
15.4 
15.4 
15.4 
15.4 
9.8 
9.8 

22.0 
19.6 
19.6 
13.0 
13.0 
12.1 



2.50 
6.25 
2.50 
6.25 
2.00 
3.50 
2.00 
3.50 

2.50 
6.25 
2.00 
3.50 
2.00 
3.50 

12.00 

20.00 

12.00 

20.00 

2.50 

2.50 

6.25 

6.25 

3.00 

3.00 

2.00 

3.50 

2.00 

3.50 

2.00 
2.00 
3.50 
2.00 
3.50 
0.65 



0.50 
1.25 
0.88 
2.19 
0.40 
0.70 
0.70 
1.23 

0.25 
0.63 
0.13 
0.23 
0.20 
0.35 

0.60 
1.00 
0.90 
1.50 
0.16 
0.25 
0.39 
0.63 
0.23 
0.30 
0.13 
0.22 
0.20 
0.35 

0.08 
0.10 
0.18 
0.15 
0.26 
0.67 



15.40 
38.50 
27.00 
67.50 
12.60 
21.53 
21.55 
37.80 

7.70 
19.25 
4.00 
7.00 
6.16 
10.80 

18.50 

30.80 

27.70 

46.20 

4.80 

7.70 

12.00 

19.25 

6.95 

11.55 

3.85 

6.78 

6.16 

10.80 

2.40 
3.00 
5.50 
4.60 
8.10 
2.00 



1 3.080 hro 



502 



ENGINEERING OF POWER PLANTS 



Type of plant and fuel 



Fuel per 
b.hp.-hr. 


B.t.u., 
b.hp.-hr. 


Therm. 

effi., 
per cent. 


Price of 

fuel, 
dollars 


Fuel cost, b.hp. 


Hour, 
cents 


Year.i 
dollars 


Cu. ft. 












11.25 


11,000 


23.1 


0.10 M 


0.123 


3.79 


11.25 


11,000 


23.1 


0.30 M 


0.37 


11.40 


20.00 


12,000 


21.2 


1.50 M 


1.50 


46.20 


20.00 


12,000 


21.2 


LOOM 


2.00 


61.60 


1.00 pt. 


18,000 


14.1 


0.04 gal. 


0.50 


15.40 


1.40 pt. 


25,000 


10.2 


0.04 gal. 


0.70 


21.55 


1.00 pt. 


12,200 


20.8 


0.15 gal. 


1.88 


58.00 


1.00 pt. 


12,200 


20.8 


. 30 gal. 


3.75 


115.00 


1 . 00 pt. 


9,000 


28.3 


0.40 gai: 


5.00 


154.00 



Gas and oil engines 

Natural gas 

Natural gas 

Illuminating gas. . 
Illuminating gas. . 

Crude oil ; 

Crude oil 

Gasoline 

Gasoline . 

Denatured alcohol 



In connection with the cost of fuel it is interesting to examine the 
Government tests of small pumping plants in California. 

Gasoline Engines and Centrifugal Pumps 





Discharge, 

gal. per 

min. 


Useful 

water, 

hp. 


Total cost 
of plant, 
dollars 


Cost per useful water hp.-hr. 


horsepower 


Fixed 

charges, 

cents 


Gasoline, 
cents 


Attendance 

and repairs, 

cents 


Total, 
cents 


3 
11 
11 
11 
15 
21 
25 
30 
30 
35 


32 
112 
147 
148 
224 
359 
635 
399 
608 
592 


0.145 
0.850 
1.65 
2.00 
2.46 
5.63 
7.65 
8.06 
10.43 
13.51 


1,075 
3,056 
1,200 
2,000 
3,500 
2,300 
3,500 
3,343 
3,000 


2.530 
1.235 
0.200 
0.387 
0.257 
0.036 
0.080 
0.136 
0.044 


0.166 
0.075 
0.029 
0.032 
0.024 
0.019 
0.018 
0.016 
0.020 
0.016 


0.121 
0.042 

0.002 

0.012 
0.001 
0.009 


2.605 

1.285 

2.74 

0.411 

0.278 

0.054 

0.108 

0.157 

0.069 



Incidentals, Etc., for These Pumping Engines.— The repair bills, etc., 
reported for these engines are very small, as indicated below. For one 
plant consisting of a 23-hp. gasoline engine, single centrifugal pump, a 
10-in. well 385 ft. deep, supplying 458 gal. per minute under a 58-ft. 
head, the total cost of engine and pump, entirely installed with belt and 
ready to run was $1,382. (This does not include well, pit, building, etc.) 

The reported repairs, etc., are: 
Incidentals, oil and repairs for 1900 
Incidentals, oil and repairs for 1901 
Incidentals, oil and repairs for 1902 
Incidentals, oil and repairs for 1 903 
Incidentals, oil and repairs for 1904 

Average 
» 3,080 hr. 



$36 . 15 = 2 . 61 per cent, of cost 
13 . 50 = 1 . 02 per cent, of cost 

23 . 30 = 1 . 69 per cent, of cost 
54 . 78 = 3 , 97 per cent, of cost 

24 . 65 = 1 . 78 per cent, of cost 
$30.00 = 2.21 per cent, of cost 



i 



EFFICIENCIES AND OPERATING COSTS 



503 



Examples of Comparative Cost of Operating Different Types of Power 
Installations. — 

Example 1. — The figures presented represent one solution for the probable cost of 
installing and operating producer gas plants in place of gasoline engines, which 
operate on distillate, for irrigation purpose in Arizona. 

The estimates are for plants of 25, 35 and 50 hp. In the table of estimates the 
plants operating on distillate are designated "D." Those operating on producer 
gas by "P-G." 

Engine Load. — Seventy-five per cent, normal rating in each case. 
Service. — Ten hours per day, 25 days per month. 

Fuel. — Distillate at 18 cts. per gallon. Anthracite at $14 per ton (2000 lbs.). 
Water. — As the installations considered are for irrigating purposes, it is assumed 
that no charge is necessary for circulating water. 

The figures given for the quantity of water used are on the assump- 
tion that this water is allowed to run to waste. 
Labor. — It is assumed that gas-producer operators are not as readily found as 
operators of gasoline engines and that a higher price must be paid for 
the former. The wages are $75 and $60 per month. 

The entire time of these operators is not required provided they can 
be near the plants, but in the cases presented it is assumed that the plants 
are isolated and that the operator has little or nothing else to do. His 
entire time is, therefore, charged to the cost of operating. Only one opera- 
tor is required for plants of the size mentioned. 
Estimate based on consumption of 1.00 pt. of distillate and 1.25 lb. of anthracite 
coal per brake horsepower-hour. 



Size of plant. 



25 b.hp. 



Type of plant. 



P-G 



35 b.hp. 



P-G 



50 b.hp. 



P-G 



Cost of plant, installed. 



Fuel, gal. and lb 

Gal. of lubricating oil 

Lb. of waste 

Gal. of circulating water. . . 

Total cost of fuel 

Total cost of lubricating oil. 

Total cost of waste 

Total cost of labor 



Operating cost only. 



$1,050 



$2,120 



$1,450 



$2,800 



$2,025 



$3,750 



Estimated total operating cost per month 



590 

8 

10 

23,500 

$106.10 

3.20 

1.00 

60.00 



$170.30 



5,850 

8 

10 

47,000 

$40.95 

3.20 

1.00 

75.00 



$120.15 



825 

10 

10 

31,700 

$148.50 

4.00 

1.00 

60.00 



$213.50 



8,250 

10 

10 

63,500 

$57.75 

4.00 

1.00 

75.00 



$137.75 



1,170 

12 

10 

47,000 

$211.00 

4.80 

1.00 

60.00 



$276.80 



11,750 

12 

10 

94,000 

$82 . 25 

4.80 

1.00 

75.00 



$163.05 



Interest on investment, 5 per cent 

Depreciation, 8 per cent 

Insurance, repairs, taxes, etc., 5 per cent. 



4.38 
7.00 
4.38 



8.85 

14.10 

8.85 



6.05 
9.65 
6.05 



11.70 
18.70 
11.70 



8.45 

13.50 

8.45 



15.60 
15.00 
15.60 



Total operating cost and fixed charges 

Total b.hp.-hr 

Total cost per b.hp.-hr., cents 

Total saving per month by installing producer-gas 

plant 

Difference in first cost. 

Months required to pay this difference by saving 

in operating expenses 



$186.06 
4,690 
3.97 



$151.95 
4,690 
3.24 



34.11 
1.070.00 



31.5 



$235.25 
6,580 
3.57 



$179.85 
6,580 
2.73 



$307.20 
9,370 
3.28 



$219.25 
9,370 
2.34 



55.40 
1,350.00 



24.50 



87.95 
1,725.00 



19.50 



504 ENGINEERING OF POWER PLANTS 

Example 2. — The problem involved in this example is to determine the relative 
cost of investment and operating cost for a gas-engine installation, operating on natural 
gas, to be capable of delivering 300 hp. to the countershafts in a machine shop. The 
four types of installation considered are: 

A. 350-hp. engine at $35 per hp $12,200 

Erecting, including air and exhaust pipe 350 

Starting devices 400 

Foundation, 100 cu. yd. at $7 700 $13,650 

225-kw. generator A.C. at $12.50 per kw 2,800 

12.5 kw. exciter 225 

Switchboard, etc 300 3,325 

Fifteen 20-hp. motors at $15.50 per hp 4,650 4,650 

21,625 

B. Two 175-hp. engines at $37.50 per hp 13,100 

Erecting, including air and exhaust pipe 600 

Starting devices 400 

Foundations, 53 cu. yd. at $7, (each) 750 14,850 

Two 110-kw. generators at $19 per kw 4,200 

- Two 10-kw. exciters 380 

Spring coupling 300 

Switchboard, etc. 400 5,280 

Motors as in "A".. 4,650 

24,780 

C. Three 125-hp. engines at $40 per hp 15,000 

Erecting, including air and exhaust pipe 800 

Starting devices 500 

Foundations, 40 cu. yd. X 3 at $7 540 17,140 

Three 75-kw. generators at $23.40 per kw 5,250 

Three 6-kw. exciters 390 

Two spring couplings , 500 

Switchboard, etc 6,640 

Motors as in "A" 4,650 

28,430 

D. Fifteen 20-hp. engines erected on purchaser's 

foundations, at $43.50 per hp 13,050 

Foundations, 16 at $50 each 750 

$13,800 



EFFICIENCIES AND OPERATING COSTS 



505 



Estimated Operating Cost per Month. — The operating cost of these installations 
is given for three sets of conditions, the load on the engines being so changed that 
it modifies the operating costs as shown. "A," *'B," "C," and '*D" represent the 
four types of installations indicated on page 496. 

Service, 9 hr. per day for 25 days. 

900 B.t.u. gas at 30 cts. per 1,000 cubic feet. 

Oil at 35 cts. per gallon. 

Waste at 7.5 cts. per pound. (The engineer of this plant is exceptionally eco- 
nomical in the use of waste.) 

Water at 5 cts. per 1,000 gal., 6, 7, 10 gal. per horsepower-hour. 

Labor for "A," ''B," "C," 2H hr. only per day at 35 cts. per hour. 

This plant has a chief engineer now who can run the gas engines if installed in 
the central plant. The only labor that must be added for ''A," "B," "C" is enough 
to look after the motors. 

For "D" it will be necessary to have an engineer at $100 and assistant at $60 
per month. 



A 


B 


C 


D 


Sogine load, b.lip 


350 

100 

11,000 


350 

100 

11,000 


350 

93.5 

11,000 




280 


Per cent, engine rating 


93.5 


B.t.u. per b.hp.-hr 


12,000 


Gas, ou. ft. 


Amt. 
965 M 

60 

25 
273 M 


$ 

289.00 

17.50 

1.88 

23.65 

19.70 


Amt. 
965 M 

75 

35 
550 M 


$ 

289.00 

26.25 

2.52 

27.50 

19.70 


Amt. 
965 M 
100 

45 
550 M 


$ 

289.00 

35.00 

3.38 

27.50 

19.70 


Amt. 
840 M 
175 
150 
630 M 


$ 

252.00 


Oil, gal 


61.25 


Waste, lb 


11.25 


Water, gal 


31.50 


Labor 


160 00 








Operating only . . 




261.73 
72.00 

170.50 
54.25 




365.07 
82.50 

206.50 
61.90 




374.58 
95.00 

237.00 
71.20 




516 00 


Interest at 4 per cent. 








48.30 


Depreciation 10 per cent 








121.00 


Repairs, etc., 3 per cent 






(6%) 72.50 
















206.75 
658.48 




350.90 
715.97 




403.20 

777.78 




241.80 


Total operating cost 








757 80 











Saving in operating expense per 
month compared with " D " 

Do. per year 

Excess first cost over " D " 

Time to make up diff. by saving in 
operating expenses 



99.32 
1.192.00 
7,125.00 



41.83 

502.00 

10,080.00 

20.5 years 



- 19.98 
-240.00 
16.930.00 



506 



ENGINEERING OF POWER PLANTS 



Engine load, b.hp 

Per cent, engine rating. 
B.t.u. per b.hp.-hr 



250 
71.5 
12,500 



250 
71.5 
12,500 



250 
2-100 
11,000 



195 
65.0 
13,900 



Gas, cu. ft. 

Oil, gal 

Waste, lb.. 
Water, gal. 
Labor 



Amt. 
780 M 
40 
25 

338 M 



$ 

234.00 

14.00 

1.88 
16.90 
19.70 



Amt. 
780 M 

60 

35 
394 M 



$ 

234 . 00 

21.00 

2.62 

19.70 

19.70 



Amt. 
688 M 

70 

45 
394 M 



$ 

206.00 

24.50 

3.38 

19.70 

19.70 



Amt. 
678 M 
130 
150 
438 M 



$ 

203.00 
45.50 
11.25 
21.90 

160.00 



Operating only 

Fixed charges 

Total operating cost 

Saving in operating expense per month 
compared with "D " 

Saving in operating expense per year com- 
pared with "D" 

Excess of first cost over "D" 

Time to make up difference by saving in 
operating expenses 



286.48 
306.75 
593 . 23 

90.22 

1,088.00 
7,125.00 



297.02 
350 . 90 
747.92 

35.53 

426.00 
10,280.00 

24 years 



273.28 
403 . 20 
676.48 

6.97 

84.00 
13,930.00 



441.65 
241.80 
683.45 





A 


B 


C 


D 


Engine load, b.hp 


175 

50 

14,700 


175 

100 

11,000 


175 

2-70 

12,800 


130 




43.7 




16,000 






Gas, cu. ft 


Amt. 
644 M 

35 

25 
236 M 


$ 

193.00 

12.25 

1.88 
11.80 
19.70 


Amt. 
481 M 

45 

35 
236 M 


$ 

144.00 

15.75 

2.62 

11.80 

19.70 


Amt. 
561 M 
55 

45 
276 M 




$ 

168.00 

19.20 

3.38 

13.80 

19.70 


Amt. 
525 M 
100 
150 
295 M 


$ 

157 . 50 


Oil, gal 


35.00 


Waste, lb. . . 


11.25 


Water, gal 


14.75 


Labor 


160.00 






1 






238.63 
306.75 
545.38 

74.92 

899.00 


193.87 
350.90 
344 . 77 

75.53 

906.00 


224.08 
403 . 20 
627 . 28 

3.02 

36.00 


378.50 


Fixed charges 


241.80 


Total operating cost. 


620 . 50 


Saving in operating expense per month 




Saving in operating expense per year com- 
pared with "D" . 




Time to make up difference by saving in 
generating expenses 


7.9 : 


>rears 


11.4 


years 











Example No. 3. — Producer-gas and steam installations. 

Size of plant 600 hp. 

Type of plant Gas Steam 

Cost of plant. $48,000 $40,000 



6,000 hp. 
Gas Steam 

$420,000 $420,000 



EFFICIENCIES AND OPERATING COSTS 



507 



Estimated operating cost 

Service 24 hr. X 300 days 

Load on engine 75 per cent, for 10 hr. 

33.3 per cent, for 14 hr. 
Tons of coal 1,300 3,000 

$2.75 gross ton 

Gallons of oil 1,200 at 30 cts. 

Pounds of waste 2,000 at 7 cts. 

Engine-room labor 2 eng. at $17 wk. 



Gas house and boiler room labor. . 2 men at $15 wk. 

Extra cleaning $4 . 50 wk. 

Gallons water (5 cts. per M) 18,000 M 125,000 M 

Gallons wasted = 20 per cent 3,600 M 35,000 M 

Total cost of 

Coal $ 3,630 8,250 

Oil $ 360 360 

Waste $ 140 140 

Engine-room labor $ 1,768 1,768 

Gas-house and boiler-room labor. . $ 1,560 1,560 

Extra cleaning $ 234 

Water $ 180 1,250 

Operating expenses only $ 7,922 13,328 

Fixed charges at 17 per cent $ 8,160 6,800 

Total operating cost $16,082 20,128 

Total kilowatt-hours 1,555,000 

Cost per kilowatt-hour $ 1 . 04 1 . 30 

Total saving per year by operating 

producer gas plant $ 4,946 

Difference in first cost $ 8,000 

Years required to pay this differ- 
ence by saving in operating 
expenses 2 



24 hr. X 365 days 

75 per cent. 
21,000 42,000 

$2.50 gross ton 
10,950 at 30 cts. 
5,000 at 7 cts. 

1 ch. eng., $100 mo. 
3 asst. eng., $17 wk. 

3 oilers, $12 wk. 

2 men at $50 mo. 

4 men at $45 mo. 



246,000 M 
49,200 M 



52,500 

3,285 

350 

5,720 

3,600 

2,460 



1,500,000 M 
300,000 M 



105,000 

3,285 

350 

5,720 

3,600 

15,000 



67,915 132,955 

71,400 71,400 

139,315 204,355 

26,000,000 

0.536 0.780 

65,040 



Cost of Steam and Blast-furnace Gas Power. — To give an approxi- 
mate idea of the relative cost of producing electric power in blast-furnace 
gas-engine and steam-turbine plants in this country, Mr. H. J. Freyn 
has published the following data from eight steam-turbine stations and 
eight blast-furnace gas-engine plants. 



508 



ENGINEERING OF POWER PLANTS 



Comparison of Cost of Producing Electric Power in Steam and 
Gas Power Plants 

All cost figures in cents per kilowatt-hour 

8 steam-turbine plants 8 blast-furnace gas-engine plants 



No. 



Item 



1 
Max. 



2 
Avg. 



3 

Min. 



4 
Max. 



5 
Avg. 



1 Plant capacity in kw 126,000 55,000 



10,000 50,000 



2 Use factor, per cent 33.3 

3 Labor 0.1730 

4 Repairs and maintenance. 0.0740 

5 Lubricants 0.0096 

6 Water '. 0.0305 

7 Miscellaneous 



25.0 



% 



0.0902 58.1 

0.0422 27.3 

0.0054 3.5 

0.0143 9.2 

0.0029 1.9 



10.0 
0.0434 
0.0250 
0.0020 
0.0020 



71.5 
0.0881 
0.1282 
0.0237 
0.0162 



11,600 
49.0 



Min. 

1,500 
, 22.0 
0.0550 33.0 0.0302 
0.0733 44.0 0.0273 
0.0125 7.5 0.0054 
0.0120 7.2 0.0036 
0.0137 8.3 



8 Totalnet operating % % 

expense 0.2414 33.3 0.1550 100.0 0.0850 0.2438 52.2 0.1665 100 0.0824 

9 Cost of 1 million B.t.u., 

cents 11.10 % 8.80 5.20 10.37 % 8.11 5.89 

10 Cost of fuel 0.3960 66.7 0.3100 0.1950 0.2441 47.8 0.1530 0.0963 



11 Total cost of power pro- 

duction without fixed 
charges 

12 Heat consumption per 

kw.-hr., B.t.u 46,400 

13 Thermal efficiency, per 

cent 11.49 



100.0 0.4650 



35,400 



9.65 



29,700 
7.35 



100.0 0.3195 
26,000 18,400 16,200 

21.0 18.54 13.12 



14 Ratio of plant capacities. 

15 Ratio of use factors 

16 Ratio of net operating ex- 

penses 

17 Ratio of cost of 1 million 
B.t.u 

18 Ratio of fuel expenses. . . . 

19 Ratio of actual fuel cost. . 

20 Ratio of total cost of pro- 

duction 

21 Ratio of heat consump- 

tion 

22 Ratio of thermal efficiency 



0.397 
2.130 



1.010 



0.560 
1.830 



0.212 
1.960 



1.074 



0.678 



0.520 
1,923 



0.150 
2.20 



0.970 



0.934 0.922 1.132 

0.617 0.493 0.494 

0.560 0.536 0.436 



0.545 
1,785 



Mr. Freyn also published the following figures of ''actual total" 
operating cost of a 40,000-kw. blast-furnace gas-engine plant and of a 
49,000-kw. steam-turbine plant for which the use factor happens to be 
exactly the same. 

All items are directly comparable since the fuel cost for the steam- 
turbine plant was corrected for coal of 10,500 B.t.u. per pound at $1.80 per 
long ton, which is the basis for valuation of blast-furnace gas in this gas- 
engine plant. 



EFFICIENCIES AND OPERATING COSTS 



509 



Comparison of Cost of Producing Electric Power 
All cost figures in cents per kilowatt-hour 





Gas-engine plant 


Steam-turbine plant 


Year 


1910 
40,000 
116,535,000 
33.3 
% 
0.0678 52.0 
0.0366 28.0 
0.0116 9.0 
0.0074 6.0 
0.0064 5.0 


1910 




49,000 




142,835,000 




33.3 


Net operating expenses: 


% 
0.0528 52.0 




0.0326 32.0 




0.0024 2.5 


Water 


0.0073 7.0 


JVIiscellaneous . 


0.0066 6.5 






Total 


0.1298 100.0 0.1298 40.0 
9.51 

0.1951 60.0 


0.1017 100.0 0.1017 23.0 


Cost of 1 million B.t.u 


9.9 


Fuel cost 


. 3400 77 . 


Total cost of power production (without 




0.3249 100.0 
19,5001 
17.51 


0.4417 100.0 


Heat consumption B.t.u. per kw.-hr 

Thermal eflBciency, per cent. . . 


35,200 
9.7 







Actual Fuel Consumption and Cost of Operation of Existing Plants. — 

The following tables and diagrams were taken from Neuere Kraffanlangen 
by Prof. Josse and were calculated from data secured by the author from 
manufacturing plants, plants of business houses and electrical stations — 
principally the latter. They show what may be regarded as average re- 
sults of German practice in 1911. 

The results for the individual plants differ materially due to the con- 
struction of the engine plant, its maintenance, operation and the number 
of employees. Interest and amortization expense are not considered 
because these depend upon local conditions. 

In Table 1 are given, for reciprocating engine plants of capacity 
less than 1,000 kw., the maximum continuous load, the plant cost, yearly 
load, thermal efficiency and the cost of fuel, lubricants, packings and 
supplies, maintenance and total cost. 

Table 2 gives a similar tabulation in so far as data are available for 
locomobiles. 

Table 3 gives a similar tabulation for two small turbine plants! 

Steam-turbine plants of small capacities are still hard to find. The 
thermal efficiency is good (0.08-0.09) with a total cost of 1.56 cts. per 
kilowatt-hour. The reason is due more to the fact that the turbines are 
in modern plants and require less maintenance than to any thermal 
superiority of the turbine. 

1 Approximate. 



10 



ENGINEERING OF POWER PLANTS 



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EFFICIENCIES AND OPERATING COSTS 



511 



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EFFICIENCIES AND OPERATING COSTS 513 

Table 4 shows results for large steam plants (of over 1,000-kw. 
capacity). In such plants more reciprocating engines than turbines are 
found. 

Table 5 gives results for steam-turbine plants of more than 1,000-kw. 
capacity. Lubrication expense is reduced and the cost of fuel and wages 
determine the cost of operation which in one plant is reduced to 0.525 
cts. per kilowatt-hour with a thermal efficiency of 12.3 per cent. 

Table 6 gives a tabulation for gas power plants. These costs differ 
depending on the fuel used. Most plants use anthracite or coke or both, 
the specific cost being lower with coke. Reliable information was not 
available of plants using lignite briquettes, but these are somewhat under 
those for coke. Gas plants are thermally superior to steam plants. The 
diversity in the specific cost of fuel is partly explained by the difference 
in price. The cost of fuel decreases as the load increases only up to 
300,000 kw.-hr. yearly load, and the expense of fuel is independent of the 
size of plant. 

The fuel cost varies for two similar plants of the same yearly load 
from 0.38 ct. to 0.88 ct. per kilowatt-hour. The cost of maintenance and 
the cost of lubrication are about the same as for the steam plant. For 
small gas plants the maintenance cost is greater than for the steam plant, 
but for a yearly load of 700,000 kw.-hr. the costs remain below that for 
steam plants. The total costs vary from 1.5 cts. to 2.66 cts. per kilo- 
watt-hour. At about 600,000 kw.-hr. the total operating cost is about 
1}4 times the fuel cost. Up to 10 years ago there were no gas engines 
built of more than 1,000 hp. capacity. Now there are more than 
1,000,000 hp. in operation in the world. Two fuels are in common 
use: Blast-furnace gas and coke-oven gas. 

In Table 7 are given the operating results for two large gas-engine 
plants. This sort of information is difficult to secure as these plants are 
just beginning to arrange for the exact measurement of gas used. The 
total cost is low, ranging from 0.264 ct. to 0.357 ct. 

In Table 8 are shown Diesel engine results. The thermal efficiency 
is nearly the same for all the plants (about 31 per cent.) with the excep- 
tion of the smallest. The cost of lubricants, etc., is somewhat higher 
than for steam and gas plants. The maintenance can be almost neg- 
lected. The unit costs for salaries decrease inversely with the yearly 
load. In general they require more skilled attendance. The total cost 
of operation amounts to 1.79 cts. for small plants and falls to 1.095 cts. for 
a plant with a yearly load of 1,000,000 kw.-hr. The total cost amounts 
to 1.7 times the fuel cost for plants of large size and about double the 
fuel cost for small plants. 

Fig. 185 shows, in the lower half of the diagram, how the total operat- 
ing costs and the fuel costs for steam, gas and Diesel engines compare. 



514 



ENGINEERING OF POWER PLANTS 















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518 ENGINEERING OF POWER PLANTS 

In the upper portion the cost for wages, maintenance, lubricants, etc., 
are expressed in percentage to the total cost for each of these types of 
engines. The gas engine shows the smallest fuel expense; the Diesel 
engine the smallest total operating expense, the steam-engine plant being 
in both cases the most expensive. In the upper chart, the Diesel engine 
is the lowest and the gas engine the highest. 



CHAPTER XXIV 
COMPRESSED AIR 

Compressed air is used for transmitting power, for the storage of 
energy for many purposes, and for producing refrigeration. Air at mod- 
erate pressures is used in blast-furnace work and in the Bessemer process; 
air at higher pressures for the transmission of power, the operation of 
cranes, hoists and presses, and for the working of motors such as drills, 
coal-cutting machinery, hoists, street cars and similar applications. 
High-pressure air has been used for storage, for refrigeration and in cer- 
tain chemical processes. Air at low pressures, between atmospheric and 
5 or 6 lb. per square inch, produced by centrifugal fan blowers or the so- 
called positive blowers, is used for the ventilation of mines, buildings and 
ships and for producing forced and. induced draft for steam boilers. The 
storage of energy by compressed air usually differs from the transmission 
of power, in that the compressed air, which is forced into the receiver at 
high pressure, is generally used at a much lower pressure in the air motor. 

Although compressed air has been used in engineering operations for 
a period of probably 200 years, the modern application of compressed air 
is probably due to Messrs. Kraft and Sommeiller whose extensive experi- 
ments at the Cockerill works at Seraing in Belgium, resulted in the use 
of compressed air at the Marie colliery in Seraing in 1856. The Som- 
meiller compressor built by the Cockerill Co. compressed the air for the 
work in the Mount Cenis tunnel in 1861. The air pressure used was 106 
lb. per square inch and the longest transmission lines exceeded 20,000 ft. 
The air motors worked expansively, the cylinders being heated to prevent 
freezing. The Sommeiller compressor (see Fig. 269) consisted of a 
plunger working between two containers filled with water, the water 
serving to cool the air and acting as the piston of the compressor. These 
compressors were quite economical and more modern constructions on 
the same principle, such as the Leavitt compressor at the Calumet and 
Hecla copper mines, have given very good service. This compressor has 
double-acting cylinders, 60 by 42 in. and runs at the comparatively high 
speed of 25 r.p.m. About 1868 the dry compressor came into use, the 
cooling being imperfect. This was improved shortly afterward by the 
introduction of the spray injection by Prof. Colladon. Spray injection 
is now no longer used and both cylinders and pistons are water-cooled to 
reduce the loss by heating as far as possible. It was soon found that it 

619 



520 



ENGINEERING OF POWER PLANTS 



was much better to make the compressor a compound or two-stage 
machine and to install intercooling coils between the cylinders. Modern 
air compressing dates from about 1877, when Mekarski and Popp com- 
menced the installation of compressed-air plants for the driving of railways 
and the distribution of power. In the United States the development 
of compressed air has followed the development of the mining industry, 
and most of the compressors have been built and sold for the working of 
air drills and similar machinery in the mining and quarrying fields. 
About 15 years ago the "pneumatic tool" came into the market and since 




Fig. 269. — Sommeiller hydraulic compressor. 

that time no shop or manufactory is complete without its compressed-air 
line, which supplies power for the use of an infinite variety of tools. 
Kraft in the years 1854-8 used compressed air for the cranes at the Cocke- 
rill works at Seraing and many of these cranes are still in use. Pneumatic 
lifts and cranes are now installed in many places. 

Air-compression machinery may be divided into (a) piston com- 
pressors and blowing engines; (6) rotary blowers of the positive-pressure 
type ; (c) centrifugal blowers or fans including the turbo-blower and com- 
pressor; and {d) the hydraulic air compressor. 

Piston Compressors and Blowing Engines. — Piston compressors and 
blowing engines differ only in the pressure to which they work. Blowing 
engines for the blast furnace usually work from 8 to 15 lb. per square inch 
above the atmosphere. Blowing engines for the Bessemer converter 
work between 18 and 35 lb. gage. Ordinary air compressors of the piston 
type for power purposes are usually built to deliver air between 50 and 
80 lb. per square inch for single-cylinder compression. From about 70 
to 120 lb. per square inch they are usually compounded and for higher 



COMPRESSED AIR 



521 




Fig. 270. — Riedler valve. 



P 



pressures, up to 2,000 to 2,500 lb. per square inch, three- and four-stage 
compression is used with intercoolers between each two stages. The 
construction is practically that of a steam engine, Fig. 269, the only differ- 
ences being the unusual care taken with the jacketing and intercoolers, the 
excessively small clearance and the type, location and area of the valves. 
The early air compressors used the standard steam-engine valves with 
the consequence that the volu- 
metric efficiencies were in many 
cases below 50 per cent. This 
almost immediately led to the 
use of poppet discharge valves 
and very large mechanically 
moved inlet valves, and finally to 
mechanically controlled valves of 
very large area for both suction 

and discharge. The well-known Reidler valves, Fig. 258, were invented 
for this use. These valves, however, have been superseded on the more 
modern machines by a very light spring-controlled multiported diaphragm 
valve, known as the Borsig type, Fig. 259, which is now used by prac- 
tically all of the better class of builders on low- and medium-pressure 
work. The International Pump Co. make a straight leaf valve of this 
type. For the large blowing tubs of blast-furnace and steel-mill work 

the Slick system has been 
very largely used. Here the 
cylinder heads are firmly fixed 
to the base of the machine, 
while the cylinder barrel is 
provided with slotted suction 
openings on each end and is 
moved backward and forward 
at the proper time, to ensure 
full valve opening as in Fig. 
261. The discharge valves 
are located as usual in the 
heads. Some of these blow- 
ing tubs have been built as 
large as 100 in. in diameter 
with a stroke of 7 ft. Bessemer blowing engines are usually of much 
smaller size and are built either on the Slick system or with the Borsig 
valves (see Trinks paper, vol. 33, Transactions A.S.M.E.). 

The positive pressure blower. Fig. 279, consists of two shafts carrying 
two- or three-lobed impellers running in a casing with extremely small 
^clearances. These blowers may be used up to about 15 lb. per square 
I 33 




Fig. 271.- 



^Borsig valve for blowing engines 
or air compressors. 



I 



522 



ENGINEERING OF POWER PLANTS 



inch and are built with much success in this country by such firms as 
the Connersville Blower Co. and the P. & F. M. Root Co. These blowers 




Fig. 272. — Compressor cylinder with piston intake. 



£^ 




Air Discharge 

Fig. 273.— "Slick" blowing tub. Westinghouse Machine Co. 



may be used either as blowers or exhaustors or as pumps (see Transactioni 

A.S.M.E., vol. 24, paper by J. T. Wilkin; vol. 28, paper by Gregory)] 

The centrifugal blowers are of two varieties, the volume blower, usee 



COMPRESSED AIR 



523 



exclusively for low pressures and large volumes, up to say 15 or 20 in. of 
water, and the so-called high-pressure blower or cupola blower, which 
delivers a smaller volume at pressures not exceeding 2 or 3 lb. per square 
inch. Centrifugal compressors of the 'Hurbo" variety with many stages. 
Fig. 263, may be built for use up to a pressure of about 150 lb. per square 
inch. 

Turbo-blowers and compressors are similar 
machines, differing only in the delivery pres- 
sures and the number of stages and delivery 
volume. They are usually built on the prin- 
ciple of the centrifugal pump, that is, the 
fluid to be compressed is conducted in radial 
paths, the only design departing from this 
arrangement is the Parsons, where the flow 
direction is axial. Turbo-blowers for blast- 
furnace work will deliver from 17,000 cu. ft. 
per minute to 60,000 per minute. Bessemer 
blowers deliver up to about 30,000 cu. ft. per 
minute. Turbo-compressors have in general 
a much lower capacity, not usually exceeding 
20,000 cu. ft. a minute at from 75 to 135 lb. gage. Larger turbo-com- 
pressors have been built, up to a capacity of 50,000 cu. ft. per minute. 
Steam-turbine drive is usually used where great capacity fluctuations 
obtain, whereas with constant capacity the high-speed electric motor 
is most used. With smaller outfits the steam turbine is almost 
invariably found, as with this drive higher speeds may be obtained 




Inlet 

Fig. 274. — Connersville 
blower or pump. 



I 




Fig. 275. — Rotary air compressor, turbine driven. 

and the number of stages kept down. The number of stages varies 
between one for very low-pressure machines to 28 for the higher 
pressures. Up to 14 stages compressors are usually built on one shaft 
and in one casing. With a higher number of stages two casings are 
used. All of these machines are very carefully water-cooled, but the 
cooling does not appear to be as efficient in the lower stages as in 



524 



ENGINEERING OF POWER PLANTS 



the upper ones. For high-pressure work this is a disadvantage for 
the turbo-compressor. However, the cooHng in the upper stages is so 
good that the discharge temperature of the air, when working at 
115-lb. pressure can be brought down to about 165°F. with water at the 
ordinary temperatures. A 1,000-hp. compressor, under these conditions, 
will use about 1,600 cu. ft. of water per hour for cooling. The minimum 
size of compressors, up to 100 lb., is in the neighborhood of 2,500 cu. ft. 
per minute, while for blowers at 20 lb., the minimum may be taken at 
5,000 cu. ft. per minute. The speeds of revolution run from 5,000 to 
6,000 in the smaller sizes down to 3,000 in the larger sizes of machines. 
The construction of the impellers is usually of radial buckets riveted 
between two nickel-steel disks, although cast wheels have also been used. 
Pressures up to 90 lb. have frequently been obtained in as low as 12 stages, 
but the buckets in this case were not radial. (See paper by Richard S. 
Rice, Transactions A.S.M.E., vol. 33, p. 381, for discussion of the turbine 
blower with efficiencies and costs.) 





Fig. 276. — Section of turbine air 
compressor showing water-cooling 
arrangement. 



Fig. 277.— Section of three-stage turbine air 
compressor. 



In the hydraulic air compressor, see Fig. 278, a descending column of 
water is allowed to draw into itself a certain amount of air. At the 
lowest point of the apparatus a sudden enlargement of section and change 
of direction slows down the water velocity to such an extent that the 
entrained air is set free and is collected in a pocket. This air, which is 
compressed to the pressure due to the head of water at this point, is 
piped to the surface for distribution and use. Such a plant is installed 
near Greenville, Conn., on the Quinnebaug River and has been quite 
successful. The efficiency of the apparatus is very high, but it is large 
and costly and can only be used in very advantageous locations. For an 



COMPRESSED AIR 



525 



account of the Greenville plant see Webber's paper, A.S.M.E., vol. 22, 
page 599. Frizell's paper in the Journal of the Franklin Institute, 1880, 
also contains a test on a plant of this kind, but a full discussion of the 
subject is in Parker, ''The Control of Water." 

Compressed-air motors are usually of the type of the steam engine 
but for small powers a rotary machine of the impulse turbine type has 
been used. Pulsometer, Emerson and other fluid pressure pumps are 
worked occasionally by air, especially where there is danger of flooding 
and occasionally it is convenient to use air in the ordinary duplex pump. 




Fig. 278. — Hydraulic air compressor. 

Economy in the use of air can be secured by preheating either by 
steam or outside heat or by a gas flame in the air current. Where pre- 
heating is used it may be possible to get more power out of the air than 
the work of compression and the higher the pressure and degree of pre- 
heating the larger is the saving. Where a compound motor is used as in 
some of the mine hoists both preheating and reheating may be practised 
with consequent economy. In the Porter compound mining locomotive 
the air is preheated, used in the high-pressure cylinder and expanded to a 
low temperature, possibly —30°. It is reheated by the heat of the atmos- 
phere blown through the reheater and then used in the low-pressure 
cylinder. 

Air-lift Pump. — The air-lift pump. Fig. 279, is the reverse of the 
hydraulic air compressor and finds a wide application in pumping deep 
wells. Compressed air is led through a small pipe to the bottom of the 
casing and the difference in weight between the water outside the casing 
and the mixture of air and water inside starts the well flowing. (See 
A.S.M.E. Transactions, vol. 31, page 311 and Parker, ''The Control of 
Water.") 



526 



ENGINEERING OF POWER PLANTS 



The mechanical efficiency of first-class air compressors, driven by- 
first-class steam or gas engines, is about 85 per cent. ; ordinary machines 
will run below this. The mechanical efficiency of turbo-blowers and 
compressors will usually run around 90 per cent.. The overall efficiency 
in the best machines will run from 70 per cent, downward. 




Fig. 279.— Air lifts. 




Fig. 280. ^Belt-driven duplex compressor. 

Volumetric Efficiency. — The actual capacity of compressor cylinders 
is not equal to the apparent capacity, due to the effect of clearance, heat- 
ing of the intake air and imperfect valve action. There have, been very 
few tests made to show measured volumetric efficiencies, but where they 
have been made, as in the case of the Rand mines these efficiencies were 
shown to be around 60 per cent. Standard machines should give from 



COMPRESSED AIR 



527 



85 to 95 per cent, volumetric efficiency under ordinary conditions. It 
frequently happens that the air ducts bringing the outside air to the 
intake valves of the compressors are so designed that a considerable rise 
of temperature takes place within them, together with a loss of pressure. 
Such arrangements have often resulted in the reduction of volumetric 
efficiency by as much as 15 to 20 per cent. 

Oil. — A number of explosions have taken place in air storage tanks 
and compressing cylinders due to the vaporization of the lubricating oil 
used in the air cylinders, hence the greatest care should be taken in the 
choice of the lubricant, and only the necessary quantity should be used. 
Some compressors have been lubricated with colloid graphite, and water 
lubrication has been used with success. Turbo-compressors need no cyl- 
inder lubrication and will probably be more largely used on this account. 




Fig. 281. — Tandem compound steam and two-stage air compressor straight-line type. 

The transmission of power by compressed air has been quite attract- 
ive in the past, especially where power for compression was cheap and 
abundant, and although displaced by electric transmission for many 
purposes, has still a large field for use. As the first extensive experiments 
were made at Seraing in connection with the mines, so in mining operations 
compressed-air transmission finds its greatest development today. It is 
also used for operating cranes and other machines where power is used 
only at intervals, as the condensation of steam, when used directly, 
is excessive and hydrauhc power is liable to give trouble from freez- 
ing. The first large system installed for actual commercial work was at 
Paris, where Popp in 1881 built the St. Fargeau station (2,000 hp.) and 
later the station at the Quai de la Gare (10,000 hp.). The system had 
34 miles of air mains, including 4)^ miles of 20-in. main. The losses at 
the farthest ends of these mains rarely exceed 8 lb. per square inch and 
the pressure carried was 90 lb. The system was well patronized on 
account of its convenience for delivering small powers, or in places where 



528 



ENGINEERING OF POWER PLANTS 



the cold exhaust could be used for refrigeration. The trouble from freez- 
ing was avoided by passing the air through a coil of pipe heated externally 
by a charcoal fire. A number of motors of a size exceeding 100 hp. were 
installed. At this plant it was reported that the cost of compressing 
33 lb. of air to a pressure of 90 lb. per square inch was a trifle less than 
1 ct. 

It is the convenience and safety of the transmission and storage of 
energy by compressed air which has made it so important and widespread 
a feature of modern engineering. The convenient return of the exhaust 
to the atmosphere is in many places an advantage, as in underground or 
submarine work, and the harmlessness of the air in case of accident, break- 
age or leakage, is often a valid reason for the use of air engines. 

Many of the collieries and mineral mines in this country and abroad 
have compressed-air transmissions approaching in size the Paris installa- 




FiG. 282. — Cross-compound horizontal-vertical ammonia compressor. 



tion. A coal mine producing 3,000 tons per day will use about 2,000 hp. 
in compressors and may have from 3 to 10 miles of mains depending on 
the size and depth of the workings. Some of the copper mines in the 
upper Michigan peninsula have large compressed-air transmissions, 20-in. 
pipe being used in a number of cases. 

Compressed-air System at Butte and Anaconda. — The Anacondf 
Copper Mining Co. operates 22 shafts at Butte. In 1912 they com- 
menced using compressed air for hoisting and installed a compressor 
plant electrically driven. Each compressor has a capacity of 7,500 cu. 
ft. (465 lb.) of free air (12 lb. abs.) compressed to 90 lb. gage and is run 
by a 1,200-hp. 2,200-volt synchronous motor. There are eight com- 
pressors in all. The system furnishes air for about 40,000 hp. of hoists^j 
the diversity and load factors being low. Seven of these compressors arc 



COMPRESSED AIR 



529 



run continuously the eighth being held in reserve, the excess air being 
used in the drills. About 13,500 hp. of motors are in use driving smaller 
compressors in the various mines for furnishing air for drilling and blowing 




Fig. 283. — Cross-compound air compressor. 

out the workings. There is a hydrostatic storage plant for the hoisting 
service of 66,000 cu. ft. capacity and the air is distributed by something 
over 3 miles of mains with a pressure drop of about 3 lb. Storage reser- 




FiG. 284. — Nordberg twp-stage motor-driven air compressor, Anaconda Copper Min- 
ing Co., 7500 cu. ft. free air per mine. 

voirs of about 8,400 cu. ft. capacity are installed at each of the large hoists 
to prevent excessive loss of pressure in the lines. 

After various electric systems had been considered the compressed-air 
system was installed for the following reasons : 



530 



ENGINEERING OF POWER PLANTS 



1. Total cost was lower, due to the fact that the existing steam hoists 
could be readily changed over at small expense for air working. 




Fig. 285. — Nordberg duplex-geared air hoisting engine, Mond Nickel Co. 

2. Large power storage capacity could be cheaply provided to over- 
come excessive inrush in starting. 




Fig. 286. — Straight hne air compressor, Meyer cut off. 



3. Synchronous motors could be used in the compressing plant main- 
taining the power factor and load factor at 100 per cent. 

4. Excess air could be used with great advantage in the drill system. 



COMPRESSED AIR 



531 



5. A steam drying plant in existence at each mine rendered reheating 
cheap and easy and largely increased the efficiency. 

It was found by test that from 1.4 to 1.5 kw. were used per indicated 
horsepower in the hoist. See papers by Nordberg, Gillie and Hebgen, 
Transactions A.I.M.E., vol. 46. See also paper by Pauly, Transactions 
A.I.M.E., vol. 42. 

The most modern and also the largest installation of this kind is the 
plant of the Rand Mines Power Supply Co., Ltd., in South Africa, which 
was installed in 1909-11. The compressor station is located at the Robin- 
son Central Deep, where 12 motor-driven compressors of the centrifugal 
type are installed, and in addition four turbo-compressors are installed 
at Rosherville, 5 miles away. Twenty-seven and one-half miles of main 




Fig. 287. — Tandem duplex compressor. 

piping 27J^ to 9 in. in diameter served to distribute the air to the 13 cus- 
tomers whose own mains extend throughout their underground workings. 
The larger compressors are driven by a 7,000-kw. motor and dehver 
2,900 lb. of air per minute at 100 lb. gage. The smaller compressors are 
half this size. The pipe lines have a capacity of 310,000 cu. ft. and 46,000 
lb. of air are thus stored in the hues between the pressures of 90 and 120 lb. 
(the allowable variation). The yearly output in 1914 was 2,826,500,000 
lb. of air at 34 per cent, load factor, with a maximum demand of 15,800 
lb. per minute. The air is used for operating small hoists, ore pocket 
gates, etc., for blowing out the working places after blasting and for oper- 
ating rock drills, the last being the principle use. Both the fixed- and 
loose-hammer percussive-type rock drill is used, the rock being too hard 
for rotary drill. All air is sold on meter readings, the Rand Co. supplying 



532 ENGINEERING OF POWER PLANTS 

Venturi meters and the mining corporations swinging gate meters, the 
mean of the two readings being taken. The air unit is a purely com- 
mercial unit and was fixed by local considerations at 27.441 lb. of air at 
100 lb. gage pressure, corresponding to 0.641 kw.-hr. See paper by A. E. 
Hadley, I.E.E., 1913, and paper of J. H. Rider, I.E.E., 1915; also 
Klingenberg, Bau. Groz. Elek. 

Storage of compressed air in small bulk and with little weight in 
strong tanks led to its use for street car service as early as 1878, and a 
number of street car systems were installed. In all cases these systems 
proved to be cheaper and better than the horsecar system which they dis- 
placed. The system usually used the air at about 300 lb. per square inch. 
A number of reservoirs consisting of Mannesmann bottles about 9 in. in 
diameter and 6 ft. long located under the seats, held the supply air at a 
much higher pressure, usually around 2,500 lb. per square inch. Most 
of the systems included a tank of heated water, through which the 
air was passed on its way to the motors. The system was, however, too 
costly to compete with the electric trolley system and has been almost 
entirely abandoned in the various localities where it was installed. 



CHAPTER XXV 
REFRIGERATING MACHINERY 

The use of so-called freezing mixtures for the abstraction of heat has 
been known for many years and is still used for domestic purposes and 
for a few other applications. Mechanical refrigeration had been in use 
for about 100 years when the first machine using ether was invented. 
Since that time air, water vapor, sulphur dioxide, ammonia, carbon diox- 
ide and other fluids have been used as refrigerating mediums, but today 
only air, carbon dioxide and ammonia are of practical importance. The 
two chief uses of refrigeration are for cold storage and transportation and 
the making of artificial ice. 

We may classify modern refrigerating machinery as dense-air, com- 
pression machines using carbon dioxide or ammonia and ammonia ab- 
sorption machines. The dense-air machine, used to quite an extent in 




Cooling Water 
AMMONIA OR CARBON DIOXIDE 
COMPRESSION SYSTEM 



Cooling Water 
DENSE AIR SYSTEM 



Fig. 288. 



marine practice, consists of a compressing cylinder, in which the air is 
compressed to about 225 lb., a water cooler which cools the compressed 
air, an expansion cylinder in which the compressed air is expanded to 
about 65 lb. and the refrigerating coils, where the expanded and cooled 
air absorbs the heat. This is known as the dense-air system and appa- 
ratus of economical size may be employed due to the high pressures used. 
This system is largely used for ice making and ice-box cooling on ship- 
board because of its safety (no dangerous fumes in case of leakage in 
confined spaces) but it is not efficient. 

In the compression systems using CO2 and NH3 the gas is compressed 
to such pressure that when cooled in the condenser by the cooling water 
it will liquefy. The liquid is then expanded through a valve into the 
refrigerating coils where it absorbs sufficient heat to evaporate the liquid 

533 



534 



ENGINEERING OF POWER PLANTS 



and the gas is then led to the suction side of the compressor to again begin 
the cycle. 

These machines are much more efficient than the dense-air machine 
and with COo pressures as high as 900 lb. must be used. The latter are 
largely employed in marine practice especially in the frozen-meat trade. 
An additional reason for their use is the fact that they can be applied to 
the extinguishing of cargo or bunker fires. The ammonia compression 
machine is used on land to a much greater extent than the others and 
more economical results are obtained than with the CO2 or dense-air 
systems. The ammonia used is anhydrous and the only serious troubles 



Brine Tank 



Cooling 
i In 



ng Water 

let 



Absorber 



UV] Expansion Yalve 



rl^ 



W 



\zy 



Pump 




Interchanger- 
"^ ) Rectifier 



Condenser 



r^4= 



Separator 



% 



/V. 



Cooling Water Outlet | , 

Analyzer- 



Steam Coils \ 



Generator 



- Fig. 289. — Absorption system. 

come from leakage of ammonia into the air and water into the ammonia. 
A tight system will avoid these troubles. 

In the ammonia-absorption system a solution of NH3 in water is used. 
The strong NH3 solution is heated by steam coils in the generator, and 
the NH3 driven off at a pressure of about 150 lb. The gas passes through 
the analyzer and rectifier and then to the condenser where the ammonia 
is liquefied by the cold-water circulation. The liquefied ammonia is ex- 
panded through the cooling coils to the absorber in which the evaporated 
ammonia is absorbed by water thus keeping a low pressure in the coils. 
The liquor is then pumped to the generator to go through the cycle again. 
This system is not efficient in small units and is better adapted to re- 
frigerating than to ice making. Many of the large systems in abattoirs, 



REFRIGERATING MACHINERY 535 

cold-storage plants and central stations for refrigeration are of this type. 
The efficiency of the ammonia absorption and compression systems are 
practically equal under commercial conditions. 

In the direct-expansion system the refrigerating fluid is circulated in 
the cold room in pipes but when air is the medium the room becomes part 
of the system. This system is comparatively little used on account of 
the regulation troubles, presence of moisture and difficulties of leakage 
when CO2 or NH3 is the medium. 

The more usual and better system is the brine circulation system in 
which the expansion coils are submerged in a brine tank, the cold brine 
(a solution of salt or calcium chloride) being circulated by a pump through 
coils in the cold room. 

The unit of refrigeration is the "ton of ice melting per 24 hr.'^ The 
latent heat of ice is approximately 144 B.t.u. so the ton of refrigeration = 
288,000 B.t.u. per 24 hr. or 200 B.t.u. per minute. The ice-making 
capacity is somewhat less than half this figure. 

In a refrigerating system the lower temperature is fixed by the room 
temperature required for refrigeration and the upper temperature is 
fixed by the amount and temperature of the circulating water. The 
pressures are fixed when these temperatures and the medium are known. 
In the American Society of Mechanical Engineers' rating the tempera- 
tures are taken as 0° and 90°F. and the economy is taken as the ice-melt- 
ing effect per pound of poal or per indicated horsepower. 

The usual piston displacements in the compressor per ton of rated 
capacity vary between 3.5 and 5 cu. ft. per minute and the power required 
varies from 1 to 2.5 i.hp. per ton of refrigeration. 

Good average efficiencies are about 25 lb. of ice-melting effect per 
pound of coal with either compression or absorption system. The dense- 
air machine is not nearly as efficient say 3 to 8 lb. of ice-melting effect per 
pound of coal. About twice the theoretical amount of cooling water is 
required for good work.. Practical figures lie between 1 and 3 gal. per 
minute per ton of capacity. 

Ice Making. — Artificial ice, one of the important applications of 
refrigeration, may be made either by the plate system or can system. 
In the plate system a series of compartments from 12 to 16 in. wide, 4 
to 6 ft. deep and 10 to 20 ft. long, are constructed from cast iron or steel 
plates behind which the brine circulates. A movable brine circulating 
coil is sometimes used in the center of the compartment to cool the water 
to the freezing temperature. After the freezing has begun this coil is 
swung out of the way. On the completion of the freezing process which 
may take from 30 hr. to a week warmer brine is pumped through the 
passages loosening the plate ice and the plate is lifted by a crane and 
sawed into blocks of suitable size for marketing. 



536 



ENGINEERING OF POWER PLANTS 



In the can process steel cans holding from 100 to 600 lb. of water are 
suspended in the cold brine tank. The freezing takes from 2 to 24 hr. 
and the tanks are emptied and handled by similar machinery to that 
employed in the plate system. Clear ice is obtained in both systems by 
a process of agitation. 

There is a third system in which a revolving cylinder, in which the 
brine circulates, dips in the water tank and becomes covered with ice 
crystals. These are scrapped off and pumped with some water into a 
hydraulic press which converts the slush into a cake of ice by squeezing 
out the water. It is difficult to obtain clear ice in this process. 

Cold Storage. — The brine-circulation system requires about 50 to 
100 per cent, more surface in the pipe coils than the direct-expansion 
system. For freezing fish and meat the surface may be 100 per cent, 
larger still. The following table of lineal feet of 1-in. pipe required per 
cubic foot of cold storage space has been adapted from Siebel. 







Room temperature, F®. j 


Direct-expansion system 


Size of room in 










cubic feet 


















0° 


10° 


20° 


30° 


40° 


50° 


100 


Average 


4.0 


2.0 


0.5 


0.4 


0.3 


0.2 


1,000 




1.25 


0.3 


0.2 


0.15 


0.1 


0.07 


10,000 




0.8 


0.2 


0.14 


0.1 


0.07 


0.04 


30,000 


Insulation 


0.6 


0.15 


0.1 


0.07 


0.04 


0.03 


100,000 




0.4 


0.12 


0.07 


0.05 


0.03 


0.02 



For brine circulation multiply by 1.75. 
For IJ^-in. pipe multiply by 0.8. 
For IJ^-in. pipe multiply by 0.65. 
For 2-in. pipe multiply by 0.55. 

Number of cubic feet per ton of refrigerating capacity per 24 hr. 
Direct expansion. For brine circulation multiply by 0.57. 



Size room 


0° 


10° 


20° 


30° 


40° 


50° 


100 


120 


500 


650 


800 


1,300 


2,500 


1,000 


400 


2,000 


2,500 


3,200 


5,000 


11,000 


10,000 


600 


2,500 


3,200 


5,000 


8,500 


16,000 


30,000 


800 


4,000 


5,000 


7,000 


12,000 


23,000 


100,000 


1,200 


6,000 


8,000 


12,000 


18,000 


35,000 



PROBLEMS 

103. The poultry, vegetable, meat and wine rooms on a passenger steamer occupy 
a space approximating 7,000 cu. ft. The dense-a^"r system with brine circulation is 



REFRIGERATING MACHINERY 537 

used. Assuming that a temperature of 30° is maintained, what will be the amount of 
1-in. pipe coil required, the rating of the dense-air machine and the horsepower 
required ? 

104. A cold storage company has a building 80 ft. wide, 100 ft. deep and four stories 
high. Assume one floor for machinery and 10 per cent, of the other floors for elevators 
and stairs, ceilings 10 ft. high, and a general business requiring an average temperature 
of 40° in the rooms, brine circulation system. Find the length of pipe coils, rating of 
the machine, horsepower required and amount of cooling water per day assuming a 
rise of 30°. Assuming an ammonia-compression system, find the size of compressor if 
the piston speed is 300 ft. per minute. Estimate the coal used per day. 



34 



CHAPTER XXVI 



HYDRAULIC POWER 



Although the generation of power by heat engines is a development of 
the last 200 years, hydraulic and air-power have been known and used 
for a much longer period and their beginnings go back at least to the 
Christian era. Air-power is of small relative importance, but hydrauhc- 
power, water-power, in favored localities is of great importance and must 
always be considered by the power engineer. 




BREAST WHEEL 



UNDERSHOT WHEEL 



Fia.'290. 



The potential energy of water may be measured by its weight (W): — 
the force available — multiplied by the available fall (h) — the space 
through which the force is to be exerted — or E = Wh. The theoretical 
power (horsepower) of water in motion is given by the formula hp. = 

f^rQ w 2 where V is the velocity in feet per second, W is the weight of 

water per second and g the acceleration due to gravity. For an efficiency 

of 80 per cent, this formula reduces to j^ = hp. where Q = cubic feet 

538 



HYDRAULIC POWER 



539 



per second, h = head in feet, which may be easily remembered for rough 
calculations. 

The earliest waterwheels were ''current wheels." These were large 
wheels. Fig. 290, with paddles which dipped in the stream and were turned 
by the velocity of the current. They were mainly used for raising water 
for irrigation purposes or for driving an archimedean screw. The 
efficiency was very low, 3 to 5 per cent. A few modern current wheels 
have been built and a little higher efficiencies have been secured. 

All current wheels depend on the natural velocity of the stream and 
an early improvement led the water through an artificial channel or flume 
where a greater velocity could be secured and the wheel was made with 




lozzle 

Fig. 291— Flash wheel. 



small clearance at the bottom and sides so that practically the whole of 
the water was made available to drive the wheel. This improved wheel 
was known as the ''undershot" wheel. Fig. 290, and efficiencies from 
25 to 40 per cent, were obtained. Later the bottom of the flume was 
built up with very small clearances to the height of the center of the wheel 
making the modification known as the breast wheel. Fig. 290, with 
efficiencies as high as 50 or 55 per cent. All of these wheels had straight 
buckets or paddles. Poncelet improved the breast wheel by curving the 
paddles and making them deeper and by utilizing the breast as a dam 
and allowing the water to spurt out near the lowest portion of the wheel 
increasing the efficiency to 60 to 65 per cent. 



540 



ENGINEERING OF POWER PLANTS 



Many wheels of this type were built in the eastern United States for 
sawmill work using heads up to 18 to 20 ft. The wheel was usually a 
built-up wooden wheel with flat buckets about 2 in. deep in a radial direc- 
tion by sufficient width to give the power required. A rectangular 
penstock- brought the water to the wheel level where the wooden breast 
and bottom of the penstock formed the nozzle. These wheels were 
termed ''flash wheels," Fig. 291, in the Catskills but were known by other 




Fig. 292. — Boyden-Fourneyron turbine, Tremont mills. 



names in other parts of the country. No good tests of these wheels are 
extant but fully 50 to 60 per cent, efficiency must have been secured in the 
better class of wheels. 

The ''overshot" wheel, Fig. 290, came into use soon after the under- 
shot wheel especially for slower moving mechanisms such as hammers 
and bellows for the early blast furnaces. The wheel was built with 
buckets capable of holding the water which were filled from the flume 



HYDRAULIC POWER 



541 



when they were at the top of their travel. The, weight of the water 
turned the wheel and efficiencies exceeding 85 per cent, were of ten reached. 
Very large wheels of this type have been built, some of them exceeding 
60 ft. in diameter. One of the most famous in America was the ''big" 




Fig. 293.— 14000 H.P. Pelton-Doble water-wheel unit. 

wheel of the Burden Iron Works at Troy, N. Y., which was 20 ft. wide, 
60 ft. in diameter and produced 278 hp. at 85 per cent. eflSciency (see 
Proceedings A.S.C.E., vol. 79, p. 708). 




Fig. 294. — "Free deviation" or Girard turbine. 

The turbine was invented in France and was introduced into the 
United States by Elwood Morris of Pennsylvania in 1843, but its develop- 
ment here was largely due to Uriah A. Boyden, who in 1844 designed a 
75-hp. wheel for use at Lowell, Mass. (Fig. 292). This was an outward 



542 ENGINEERING OF POWER PLANTS 

flow wheel but in 1849 J. B. Francis designed for the Boott Cotton Mills 
at Lowell the inward-flow Francis turbine, now the standard wheel for 
low-head work both in this country arid Europe. These wheels of modern 
construction give a maximum efficiency of over 90 per cent. 

The flashwheel is the probable predecessor of the impulse wheel which 
came in use shortly after 1870. The impulse wheel is a high-head type 
and the water is jetted from a nozzle into buckets on the periphery of the 
wheel (Fig". 293). These wheels are generally known as the Pelton type 
although the Pelton patent of 1880 was antedated 5 years by the Atkins 
patent which was not utilized. These wheels give an efficiency of 80 to 
85 per cent. A European type of impulse turbine which has been used 
to a considerable extent is the Girard, also known as a free deviation 
turbine (Fig. 294). The water is led inside the ring of buckets and jetted 
outward, High efficiencies have been obtained. 

Water turbines may be classified as impulse or reaction turbines with 
more justice than steam turbines, but the terms, partial intake or full 
intake, better describe the classification. They may also be classified 
as to the direction of water flow as axial or radial flow, and inward or 
outward flow, but practically all modern turbines fall into two classes, 
the inward-flow central discharge turbine, known generally as the Francis 
turbine, and the class in which a free jet impinges on an open bucket 
generally known as the tangential or Pelton type. 

With the current wheel no serious constructions were required as the 
wheel was supported by floats or cribs in the moving current of the 
stream, but with the better types of machinery flumes and masonry 
supports had to be constructed, dams became necessary to artificially 
increase the available head and to store water to secure a uniform flow. 
The study of the variation of stream flow became a necessity and rainfall 
and run-off records were kept and compared. These records are now 
made and published by the Government in the Water Supply Reports 
for the run-off of streams and by the Weather Bureau for rainfall. 

To secure stream flow or run-off records the stream must be rated 
and a gage maintained and read at least once each day usually at 8.00 
a.m. A cross-section of the strearn is chosen where the river is straight 
for a considerable distance on both sides and where the bottom and sides 
are rock or hard gravel or hard clay not liable to change during floods or 
low water. This cross-section is accurately surveyed and a gage is 
established with its zero at the lowest low-water level on record. 

Next the velocity of flow of the stream is obtained at as many gage 
readings as possible. This is usually done by means of a current meter 
(Fig. 295). The cross-section is divided into many small areas and a 
velocity reading is obtained at the center of gravity of each area. These 
readings are averaged for the mean velocity and the discharge is calculated 



HYDRAULIC POWER 



543 



in cubic feet per second for that gage reading. Where a current meter is 
not available floats or rods weighted to float in an upright position may 
be used; the velocities being obtained by timing the floats in passing a 
given distance downstream. After the discharges have been obtained 
for a number of gage heights a rating curve may be plotted connecting 
each gage height of the stream with a discharge. When the daily dis- 
charges are plotted a curve known as a hydrograph is obtained in which 
all the variation of the flow of the stream is shown graphically. The daily 
discharge is always given in cubic feet per second or cusecs. The aver- 




Lead Weight 

Fig. 295. — Current meter. 



age yearly and monthly discharges are also given as inches of water 
on the watershed or catchment area in order that they may be compared 
with the rainfall. Maximum and minimum discharges are also noted 
and stated in cubic feet per second and also in second-feet per square 
mile of catchment area. 

There have been a great many attempts to connect rainfall with run- 
off so that in the absence of long term gaging records nearly correct 
figures for a given watershed might be obtained from the rainfall records 
which usually cover a much longer period. There are a number of papers 
and much discussion of this subject in the Transactions of the A.S.C.E., 



544 



ENGINEERING OF POWER PLANTS 



1913-14 and 1915, but this method should be used with discretion and 
only when gagings are not available. 

It should be remembered that while the water flowing in the streams 
is due to rainfall, some portion of this is evaporated, much is absorbed 
by vegetation at certain periods of the year, and a considerable fraction 
may be stored in the earth for long periods. Many experiments have 
been made to ascertain these quantities under certaici conditions and 
details may be found in Rafter, ''Hydrology of New York;" Mead, 
''Hydrology;" and the Transactions of the A.S.C.E. 

Having the gagings of a stream for a number of years the mean monthly 
flows can be calculated and a curve plotted showing the summation of 
these flows. This curve is called a mass curve. See Fig. 296. A 
straight Hne passing through the origin and tangent to the lowest portion 



1905 



1906 



190.7 



1908 



1909 



1910 



1911 




ELENOR WATERSHED 



Fig. 296. 

of the curve will give the largest average flow to be obtained from the 
stream and the necessary storage can easily be calculated. It usually 
will not pay to provide this amount of storage but a discussion of the 
mass curve and a survey of the available locations for storage reservoirs 
and dams will soon show the economical size of storage and the economical 
mean flow to be provided for. The longer the set of gagings the better 
will be the work especially if they include a minimum year. It is inter- 
esting to plot the variations of the yearly rainfall for the available years 
as a curve in conjunction with the hydrographs. A study of these 
curves for any watershed will well repay the trouble. It is, however, 
important that a sufFcient number of well-located rainfall stations be 
present on the watershed or the curves will be misleading. 

The creation of a large storage reservoir is usually a costly operation 
both as to dam and land damages. The following table of the cost of 



i 



i;;2oo 



150 



100 



r 


Inches, Land Area ^ 

Feet, Gatun Area q 

GRAPHICAL SCALE 3J 

(11.624 Inches Storage on 

Water-shed Equivalent to f" 

6.67 Feet Storage on Lake O 

M Gatun at Elevation-f .87) ^ 




300 - - - 










250 


















/ 


/_ 


...._- y ,-«'* 


/ /■'-■ 


^ -, 


;^-/ 


-. :'g^ 


■, - s ^Tt^ 


j!-=ifP^C|- 


~ ' J ~ 


^ _^__4 


.. . -j_ - _ ±- 


- r- 


^ 


y'--^- --- - 






!(W ASONlojF^jAMVljlAslo^^llD.Fr, 


Time Months 




MASS CURVE 

FOR DETERMINING THE PERIOD OF LEAST YIELD 

OF THE GATUN LAKE WATER SHED FOR 1901-11 

SHOWING MAXIMUM DEPLETION THAT WOULD 

HAVE OCCURBED WITH VARIOUS RATES 

OF LOCKAGE 



(FlKifW |>0«< «44) 



HYDRAULIC POWER 



545 



large storage reservoirs has been compiled from various authorities and 
shows the extreme variations of cost. Compare the differences of the 
cost of the Ashokan and Croton reservoirs on small streams with the cost 
of the Assuan storage on the Nile. 

Cost of Storage Reservoirs 



Location 



Storage, 
billions of 
cubic feet 


Cost per 

billion, 

cubic feet 


81.0 


$238,000 


35.0 


343,000 


16.0 


792,000 


11.45 


1,560,000 


9.36 


94,000 


8.42 


269,000 


8.0 


125,000 


7.84 


973,000 


7.5 


533,000 


7.4 


21,000 


5.23 


23,000 


•4.46 


19,000 


4.27 


972,000 


3.88 


47,000 


1.74 


39,000 



Assuan, Egypt (new) 

Assuan, Egypt (old) , 

Ashokan, N. Y 

Christiana & Harts River, Transvaal 

Belle Fourche, S. D 

Wachusett, Mass 

Aziscohas, Maine 

New Croton, N. Y 

Chattanooga, Tenn. (approx.) 

Buena Vista, Cal 

Laramie River, Wy 

Indian River, N. Y 

Croton, N. Y 

Lake MacMillan, Pecos, N. M 

Bear Valley, Cal 



Dams may be classed as: 

1. Earth. 

2. Earth with core wall. 

3. Hydraulic-filled earth. 

4. Timber. 

5. Masonry. 

6. Concrete and cyclopean masonry. 

7. Hollow, Ambursen or reinforced concrete. 

8. Steel with or without rock fill. 

9. Moveable or Bear trap (barages). 

The earth dam is a simple bank of earth. The top soil is usually 
cleared away to good firm soil and then the dam is built in thin horizontal 
layers well watered and compacted by rollers as the work progresses. 
The upstream slope is usually 4 or 5 to 1 and protected by riprap or 
pitched with cobble or flagstones. The downstream slope is 2 or 3 to 1 
and is sodded. These dams should not be built over 8 to 10 ft. in height 
if they are expected to be tight and the width of the horizontal top should 
be equal to the height. Ample spillways of masonry or solid timber should 
be provided. In some localities such as irrigation work in India these 
dams have been built much higher and the percolation through the dam 
has been regulated with good success. 



546 ENGINEERING OF POWER PLANTS 

Earth dams for higher heads should be constructed with core walls to 
prevent seepage and percolation which would eventually lead to the 
destruction of the dam. The core wall may be of puddled clay, timber 
sheet piling, stone, concrete, or steel. The core should start a sufficient 
distance below the foundation of the dam to prevent dangerous seepage. 
The core must be thick enough to be impervious and should be carried 
up nearly to the crest of the dam and above the spillway level. Many 
experiments have been made to determine the line of ground water in an 
earth dam but this seems to depend on the nature of the materials, which 
should be thoroughly investigated before construction and all improper 
earth thrown away. 

At Gatun, Panama, the 30-mile lake of the Panama Canal is held back 
by the Gatun dam, a hydraulic-filled dam with rock toes and riprap 
facings. The toes were first placed of heavy rock and then soft mud and 
sand pumped in to fill the interior as the riprap slopes were carried up. 
This dam is 120 ft. high and about a mile wide. It sustains a head of 
water exceeding 80 ft. The Necaxa dam of the Mexican Light and Power 
Co. is of this type and is 190 ft. high, the highest earth dam in the world. 
It has a puddled clay core, riprap slopes and a hydraulic fill. 

Timber dams are built by sinking square cribs of timber which are 
filled with riprap to hold them in place. On these cribs the covering 
planks are laid. Another good way on a small stream is to drive a line 
of wooden sheet piling across the stream. To the sheet piling is spiked 
a 12- by 12-in. mudsill as low down as possible on the upstream side. 
Cribs of round poles are placed downstream of the sheet piling supporting, 
the wales and the cover planks are spiked to both mudsill and wales. 
The dam soon silts up on the upstream side and remains tight as long as 
the silt is there. The whole length of the dam is usually the spillway in 
which case an apron of planking is necessary on the downstream side to 
take the impact of the spill water and prevent undercutting. 

Masonry dams built of brick or cut stone are of all sections, the plain . 
rectangular wall with a capstone sloping downward upstream being very 
common for low heads. The best form for a masonry dam is dependent 
on the kind and weight of the masonry and whether it is also to be used 
for a spillway. For this purpose the ogee form is the most frequently 
adopted as giving the maximum effect with the smallest cost and such 
dams are often submerged 10 to 15 ft. without danger. Masonry dams 
are rarely built except upon a rock foundation. 

Concrete may be used instead of masonry or the so-called cyclopean 
concrete in which very large stones often exceeding 10 tons are imbedded 
in the concrete. It is said to be important that these stones do not 
touch but at least one large dam was constructed by piling up the large 
stones in the forms and then grouting the pile thoroughly. This con- 



HYDRAULIC POWER 



547 



struction cannot be recommended. Small dams have been Luilt of rein- 
forced concrete in sections similar to a retaining wall but for large con- 
structions and a solid dam steel reinforcing is not necessary. All masonry 
and concrete dams should go deep enough into the solid rock to prevent 
failure by shear or moving bodily downstream. In the dam at Austin, 
Texas, which failed by moving downstream, the toe was at the upstream 
end of the section and was only 24 in. wide. The dam at Austin, Pa., 
failed in the same manner. 




JFiG. 297.- 



-Section of Estocada dam and power house, Portland Railway Light & 
Power Co., Ore. 



The hollow or Ambursen concrete dam is usually built "A" section 
in bays of proper width and the usual design of reinforced-concrete struc- 
tures is followed. The design has been criticised by some engineers who 
maintain that concrete under water is not sufficiently impervious to pre- 
serve steel from deterioration but the oldest Ambursen structures have 
shown no sign of deterioration up to date. In this type of dam the power 
house may be placed in the interior of the dam and remarkably economical 
construction results. 

Steel dams are of two types. The commoner consists of a set of "A" 



548 ENGINEERING OF POWER PLANTS 

frames with buckle plates riveted to the upstream flanges. These plates 
may be protected from deterioration by a thin layer of concrete. The 
second type has been used in the rocky canyons of the Western States 
where a steel-plate core has been anchored in the side walls and bottom 
of the canyon and broken rock has been dumped on both sides of the plate 
to provide stability. In some cases the plate has been protected by a 
light concrete wall on both sides. 

The bear-trap or movable dam was developed during the canalization 
of the European rivers and has been extensively used by the United 
States Government engineers on the Ohio and its tributaries in the im- 
provement of navigation. During a flood the dam is lowered to the bot- 
tom of the river but as soon as the flood subsides the dam is raised and a 
pool sufficient for navigation is formed. The bear-trap dam consists of 
a number of units or palets about 24 in. wide and the height of the dam. 
These palets are hinged at their bottom ends to a heavy masonry construc- 
tion at the bottom of the river. At the point of center of pressure at the 
downstream side a strut is attached, which fits in a lock at the bottom of 
the river below the hinge and holds the palet in a nearly vertical position. 
In another type the strut is hinged at the downstream end and the con- 
nection of strut and palet is so placed that the unit when set up is stable 
until the water reaches a certain height when the palet is overbalanced 
and falls to the bottom. Other types have ''A" frames supporting a 
platform and longitudinal girders on which square logs of wood are sup- 
ported. These are removed by the attendants in time of fiood and re- 
placed afterward. 

Spillways. — Every dam should be provided with a spillway of suffi- 
cient capacity to take care of the maximum flood. Frequently the whole 
crest of the dam is used as a spillway as at Holyoke and Hales Bar and 
such dams must be made heavy to prevent overturning when the water 
is at its maximum height above the crest. Where the floods are of smaller 
moment a portion of the crest is made lower and walled in at the sides to 
act as a spillway as at the Delta and Hinckly dams, N. Y. The spillway 
is often placed at a distance from the main dam where rock is available 
and a first-class construction secured at less cost, as at Ashokan, N. Y. 
Where floods are severe and of very rapid rise it is common to provide 
a small spillway for normal use and to install gates of sufficient size in 
the dam itself to take care of the flood waters. Examples of this type of 
construction may be seen at Chevres on the Rhone, Switzerland, where 
large gates of the "Stoney" type are in use and at the Scotland Dam on 
the Shetucket, Conn., where gates of the ''Taintor" variety are installed. 
It is usual to allow a rise of about 5 ft. over the crest of the spillway at 
maximum floods. 

During ordinary seasons the crest of the spillway is increased in height 



HYDRAULIC POWER 



549 



-1 Iron Rod 



by flashboards. The simplest construction consists of pieces of ordinary 
pipe 10 ft. apart imbedded about 1 ft. in the concrete crest of the dam. 
Into these pipes, pieces of round iron 1 in. to 1)4 in. in diameter and ex- 
tending in some cases 3 ft. above the crest, are inserted. On the upstream 
side of these rods pieces of 2 by 12-in. planking are laid on edge thus raising 
the crest 3 ft. (see Fig. 287) . The planks are 
held in place by the water. In case of a —^"^£^^^5 
sudden flood topping the crest the iron rods 
bend over, allowing the planks and water to 
escape down the spillway. There are a num- 
ber of patented flashboard constructions but 
the commoner type is the best and cheapest. 
Hydraulic-station Layouts. — Hydraulic- 
station layouts are almost always determined 
by the physical conditions of the case in 
question, since the local geological condi- 
tions usually determine the site of the dam 
and power house, the quantity of water and head available. At times 
there may be a choice of types, but this usually happens only when the 
head is on the dividing line between the Pelton and Francis types, or 
when the head is so low that a number of wheels must be used on one 




fl '- .' Top" of .Spillway;- 4 . ; 



Fig. 298.— Flashboards. 




Fig. 299. — Section through penstock and power house, Uncas Power Co., Scotland, Conn. 



shaft. There always remains, however, the choice between horizontal 
and vertical shaft wheels. 

Where the stream regimen is fairly constant and the power house is a 
part of the dam itself three arrangements should receive careful considera- 
tion; the horizontal shaft wheel extending into the head race with the 
shaft parallel to the flow of the stream, and the draft tube to carry the 



550 



ENGINEERING OF POWER PLANTS 




Fig. 300. — Typical cross-section of power house, Coosa River, Lock 12 development. 



HYDRAULIC POWER 



551 



water away; the horizontal shaft wheel with the shaft at right angles to 
the flow of the stream, necessitating a penstock and with the draft tube 
as before. Both of these plans necessitate a power house below the dam, 
although the Ambursen type, with the power house inside the dam, may 
be used. Third, the vertical shaft wheel, either submerged or with a 
draft tube. Here the power house may be above the crest of the dam 
if desirable. In the first and third cases the penstock is an open one. 
In the second case the penstock is very short, sometimes only a foot or 
two longer than the wheel casing. Due to the short connection, there is 
no trouble from surges or water inertia. With higher heads, or where the 
power house is located at some distance from the dam, penstocks with or 
without canals or flumes, are necessary, and either the vertical or hori- 




FiG. 301. — Stoney gates, Manchester ship canal. 



zontal shaft wheel can be used. The two or three permissible arrange- 
ments are usually laid out and quick preliminary estimates are made to 
determine the best plan. Where plenty of water is available with low 
heads two or even three or four wheels may be used on one shaft, or a 
number of wheels may be geared to one shaft. Where there are two good 
ways of solving the problem it is sometimes advisable to secure proposals 
on both types of installation and use the most advantageous. 

Due regard should be given to the convenience of repair, which may 
well be in certain cases the deciding factor. There are certain plants in 
which it is necessary to draw down the pond 10 ft. or more in order to 
make repairs on one wheel. That plan is usually the best which puts the 
wheel above the tail water and provides a gate between the head race 
and the wheel. In good installations a turbine can be opened, examined 



552 



ENGINEERING OF POWER PLANTS 



and put back into service in less than an hour. This is not usually pos- 
sible with submerged wheels. Large headgates cannot be handled quickly 
and pumping a wheel pit is a slow and troublesome operation. 

Many installations must be built with wheel pits and submerged 
wheels. In such cases the headgates should be very carefully designed 
and, if large and heavy, cranes should be provided for their rapid and 
efficient handling. Up to a width of about 5 ft. and a head of 8 to 10 
ft., the ordinary wooden stop logs make the best and cheapest headgate 
for concrete or stone constructions. Above these dimensions steel gates 
of the Stoney type with roller supports may be used (see Broome gate, 
Fig. 302) , but the construction should be solid and in larger sizes should 




Gate Closed 



Gate Partly Opened 

Fig. 302. — Broome gate. 



be of the cellular construction used in lock gates. Where rollers are used, 
cast-iron roller races should be bolted to the concrete or stonework. 
The smaller sizes of gates are worked by the ordinary screw and winch 
handles. Many large installations are provided with the Taintor gates 
for use as headgates. These gates consist of a 30° to 60° section of the 
surface of a cylinder and are hung on a horizontal axis on the downstream 
side. They are sometimes as wide as 20 ft. and may be 8 or 10 ft. high, 
with leather or rubber washers on the sides and bottom of the gate to 
keep them watertight. They are handled with the ordinary screw 
control in the smaller sizes, or by a hoist for the larger sizes. At the 
admirable water-power installation at Chevres on the Rhone below Geneva 
these gates are used to close the wheel pits on the upstream side, and the 



HYDRAULIC POWER 



553 



sump pump is of such a size that it is possible to examine the three wheels 
on one shaft and get them back into service in less than 2 hr. 

Most rivers and lakes contain more or less floating trash, sticks, leaves, 
logs of wood, and, in the winter, ice. Suitable means must be provided 
to prevent this rubbish from entering the penstocks and wheels. Float- 
ing debris is usually controlled by a floating boom which directs this 
class of rubbish over the spillway. The rubbish which passes below the 
boom must be caught on a rack or screen. These racks are usually made 
of flat bars, set edgewise and properly spaced and stayed. They must 
be kept clean, which is usually done by means of a rake and cheap labor. 
Occasionally, as at Chevres, where the trash is troublesome and the rack 
is over 300 ft. long, a power rake electrically operated is used. This rake 




Normal Tailwater| 
EU51.0 



Corrugated Steel Sheet 1 



Fig. 303. — Tainter gates, Scotland dam. 



is on a car which travels the entire length of the screen, raking and deliver- 
ing into dump cars. The trash in this case has a fuel value and is dried 
and burned. In northern localities the same booms and screens are used 
to divert ice, and in some situations the raking must be continuous during 
the winter. At Rochester, on Brown's race, the raking for three 600-hp. 
wheels often requires three shifts of eight men for days at a time. In this 
race the ice forms on the bottom of the race as well as at the water surface, 
which makes the trouble very serious. '' Anchor ice '' is ice that forms on 
the bottom of passages or races. "Frazil ice" is fine needles of ice, 
which in certain localities form all through the body of the stream, and 
when caught in the wheel passages may freeze solid. 

Reserve. — When laying out a hydraulic power plant the question of 
reserve must be considered in connection with the expected load, the water 

35 



I 



554 



ENGINEERING OF POWER PLANTS 



•Up: 




f~^^^ 



available, and the diversity of water-supply peak and load peaks. As a 
general rule, one unit of the largest size should be installed as reserve. 
Where no water is available for reserve or where the minimum water does 
not coincide with the minimum peak, a heat-engine reserve or standby 
plant may be necessary. Many hydraulic installations require this 
heat-engine reserve, and where the variation in water supply is consider- 
able, the steam reserve may be nearly as large as the water power itself. 
At Utica the Trenton falls plant of 6,000 kw. has a steam auxiliary of 
4,000 kw. and both plants will probably be increased in the future in 
about the same proportions. There are many cities whose lighting and 
traction supplies are generated by water power, which have steam auxil- 
iaries capable of carrying the full load, in case of breakdown or low water. 
The Rochester company, taking 10,000 kw. from Niagara Falls, keeps the 
same capacity in steam power with banked fires as a standby. 

Frequently water power has been 
sold for delivery only when water 
power is available. This is known 
as secondary power and of course 
brings a lower price. There are cases 
where tertiary power is also sold, 
which may be cut off by the hydraulic 
company at any time it sees fit. 

Water Storage Batteries. — It has 
often been proposed to pump the 
tail water back into the pond by 
cheap machinery, or in the time of 
low load, and to utilize it again at 
the peak. At the Rheinfall at 
Newhausen such a water storage is 
in use. Here a fall of about 60 ft. is available but owing to state re- 
strictions only a certain portion of the water may be used. The 
load curve is of the usual light power and traction type, with about 50 
per cent, load factor. Two combination units have been installed, 
each consisting of a high-head centrifugal pump, a water turbine 
and an electrical unit capable of being used either as a motor or 
generator, all on the same shaft. The turbines in the main plant, at 
time of light load, furnish electrical energy which is used by the motor 
and centrifugal pump portion of the unit to pump water to a storage 
reservoir situated in the hills about 240 ft. above the station. When the 
peak comes on, the cycle is reversed, and the water in the reservoir is 
used in the turbine, driving the electric machine as a generator to supply 
the additional power. There are a number of these installations in 
Europe, and the idea seems to have originated with Sulzer Bros, who have 



Fig. 



*^. — J 



304- — Gelpke's standard types. 
Kaplan's types are similar. 



HYDRAULIC POWER 



555 



furnished the pumps and have charge of the installations; Escher, Wyss 
and Co. furnishing the turbine and Brown, Bouverie and Co. the electric 
apparatus. It has also been proposed to use the Humphrey pump to 
pump the tail water back into the pond, but no installations of this kind 
have been made. 

Design and Proportions of Turbines and Runners. — Gelpke in 
*'Turbinien und Turbinienlangen " has given particulars of the design of 
eight standard types of Francis wheels which are tabulated below with 
changes to suit American practice (see Fig. 293). 



Type 


c 


Rev. at 1- 
ft. head X 
diam., mD. 


V 

Z>2 


P 

Z)2 

77 = 0.8 


Gelpke's 

max. value 

of. 


Moody's best 
values of v 
(see curve) 


B 
D 


Diam. exit 

edge of vanes, 

D 


VIII 


10.8 


77 


0.222 


0.020 


0.83 


0.885 


0.08 


0.66 


VII 


13.1 


80 


0.302 


0.027 


0.84 


0.89 


0.10 


0.67 


VI 


16.6 


83 


0.441 


0.040 


0.845 


0.903 


0.125 


0.70 


V 


22.2 


89 


0.685 


0.062 


0.86 


0.915 


0.16 


0.75 


IV 


29.4 


96 


1.03 


0.094 


0.87 


0.918 


0.20 


0.86 


III 


40.6 


107 


1.58 


0.144 


0.87 


0.918 


0.25 


0.97 


II 


54.5 


121 


2.23 


0.203 


0.83 


0.91 


0.30 


1.10 


I 


70.4 


138 


2.87 


0.260 


0.77 


0.87 


0.35 


1.23 



As the speed n, horsepower, hp. and head H are known, C or the 
"unit speed," i.e., the speed which under 1-ft. head will develop one hp., 




A= S.Morgan Smith & Imp,.New American 
5 = Sampson 
C= Trump & Victor 

D=McCormick CJ.& W. Jolly & S.Morgan 

Smith) 
E= Rodney "Hunt 
F= R.Poole & Sons 



5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 
R.P.M. Under 1 Ft.Head 
Fig. 305. — Characteristic curves of standard American turbines from catalog figures. 



c 



= — tt^t— can readily be found and the type determined. If Q is 
the cubic feet per second passing through the wheel when developing 



556 



ENGINEERING OF POWER PLANTS 



HP horsepower at H head, the quantity passing at 1-ft. head is q and 
~r = P, the horsepower at 1-ft. head, if the efficiency y = 0,80. 

Let us suppose a turbine is required to give 500-hp. at 300 r.p.m. 



under a head of 50 ft. C will then be 



300 X VSOO 
50'/* 



= 50.4. This will 



indicate that a turbine of type intermediate between II and III is re- 
quired. Taking type II, mD is 121 and — — 



2.85 ft. = D. 









10 




. Type Characteristic or 
20 22.5 30 40 45 


Unit Speed 
30 60 


s. 
67 


Foot Lbs. System. 
5 70 80 90 




LOO 
















































' 






















































































































/J 


• P. 


VIor 


•is ( 


3o. 












































JJ 







- 







. 








/W 


illm 


an J 


>eav 


erl 


ilorg 


•an 










90% 




























^=^ 


^ 


^ 


















































1 


\ 


\ 


s<- 


,Sa 


nso 


tiT 


irbi 


les 








— 


■| 




^ 












>-< 


V 


■~-- 


^v 






\ 


< 




\ 


c-^ 


Sw 


;dis 


1 T 


ii'bi 


fies 






j. 


/ 


V 


Grs 


f & 


D^ 


:hoi 


na 






\ 




N 


\ 




^ 


\, 




\ 


\, 










.2 80% 




Ii 






















\ 


\, 


^ 


\ 




-^ 


S 






\ 




































\ 


N 


~R« 


ich« 


=^ 




*> ^ 




\ 






pa 








BEST REPORTED TEST RESULTS 
CURVES BY PRit)F. MOODY 
TRANS. ASCE-VOL-LXVI 






\ 


\ 


\ 




} 


Wag 


enb 


ach 


^ 


\ 


















\ 
\ 






i 


lis-bha 


mei 


s 








































V 


















10(^0 


































\ 


















































\ 

1 




















"f 


;on 


Whbels 










Fra 


ncis 


-T 


arbi 


nes 






\ 






















^\ 


Siraird \ 


Vhe 


;ls 







































































































































20 40 60 80 100 120 110 160 180 200 220 240 260 280 300 320 340 
Specific Speeds (Metric SysteiiOR.P.M. 

Fig. 306. 



380 400 420 440 460 



A wheel of this diameter at 300 r.p.m. and 50-ft. head will develop about 

P 
580 hp. at 80 per cent, efficiency, y^ = 0.203; multiplying this by 

D2 and E'^ gives 583 hp. 



Taking type III, mD is 107 and 



107 X 



300 



50 P 

= 2.52 ft. diam. jr^ is 



0.44. 144 X 2.522 X 50^' = 324 hp. This wheel is much too small. 
It will probably be possible to find a stock wheel which will more closely 
fit the conditions than type II. 



HYDRAULIC POWER 



557 



D. W. Mead has plotted the characteristic curves of the various makes 
of stock American wheels in his discussion of Larners paper in vol. 66 
of the Transactions of A.S.C.E. These curves are plotted with r.p.m. 
per minute under 1-ft. head as abscissae and hp. .under 1-ft. head as 




^0 24 28 52 J6 40 

PiscHarge in Cubic Feet per Second under One Foot Head. 



ordinates. A modified reproduction ot these curves is given in Fig. 296. 
If the efficiency is 80 per cent, the ordinates of these curves multiplied 
by 11 will give q, the quantity of water used at 1-ft. head and g at any 
other efficiency may be readily found. 



If the ''unit speed" C = 



and the head H are known it will 



558 



ENGINEERING OF POWER PLANTS 



be possible to pick out innumerable combinations of power and speed 

depending on the size of the runner used. 

Values of C from 1 to 6 or 7 indicate the Pelton or tangential type; 

from 10 to 100 the Francis type. The values between 7 and 10 indicate 

the field of the outward radial-flow turbine of the Girard type often 

called ''a free deviation turbine" and hardly known in America. 

^, ^ . ^ . , , , peripheral speed of runner 

The coemcient oi peripheral speed <b = ; = 

V2fH 

0.00653Dn 



Vh 



is a very convenient runner characteristic indicating whether 



certain high or low values of C are due more to a high or low speed (large 
or small bucket angles) or to a high or low capacity. According to 
Zowski for low-speed runners C = 10 to 28, = 0.58 to 0.7. 

Thus from C = 28 to 60 would indicate medium-speed wheels with 
values of <^ from 0.6 to 0.8. High-speed runners would have C > 60 with 
values oi (j) > 0.7. 

The square of C is called by Mead K5 = specific speed and by Parker, 
the type constant. In the Journal of Electric Power and (ras, May 25, 
Aug. 3 and Nov. 9, 1912, G. J. Henry, Jr., presents some interesting 
tables on both tangential (Pelton) and Francis wheels. He divides the 
Francis wheels into five types as in the following table: 



Types 



D 



E 



Unit speed C 

Peripheral speed 

R.p.m. at 1-ft. head. 

Q 

f full gate 

Efficiency \ ^^ gate. 

[ H gate. 



80-68 
82-79 
32-155 
2-50 + 
0.72 
0.75 
0.68 



68-50 
79-73 
26-160 
,25-45 
0.77 
0.79 
0.73 



50-38 

73-68 

20-160 

0.8-40 

0.80 

0.82 

0.76 



38-24 

68-64 

15-160 

0.5-38 

0.81 

0.83 

0.77 



24-10 

64-60 

15-160 

0.3-22 

0.80 

0.82 

0.76 



For the Pelton wheels he gives the following table where D = pitch 
diameter of buckets, d = jet diameter. 


D 

d 


10 


11 


12 


13 


14 


15 


16 


18 


22 


26 


30 


C 


5.35 


4.85 


4.46 


4.11 


3.83 


3.56 


3.35 


2.97 


2.43 


2.06 


1.79 


Efficiencies 



Full gate 
^ gate . . 
H gate . . 
M gate . . 



0.60 


0.70 


0.76 


0.79 


0.80 


0.81 


0.82 


0.82 


0.82 


0.81 


0.80 


0.83 


0.81 


0.85 


0.86 


0.87 


0.86 


0.86 


0.85 


0.84 


0.68 


0.75 


0.80 


0.82 


0.84 


0.84 


0.84 


0.84 


0.82 


0.80 


0.62 


0.72 


0.77 


0.80 


0.82 


0.82 


0.82 


0.81 


0.80 


0.77 



0.81 
0.83 
0.77 
0.73 



i 



HYDRAULIC POWER 559 

<t> for tangential wheels varies between 0.40 and 0.47. Parker in his 
*' Control of Water" gives good methods of checking up designs of both 
types of wheels. 

Moody in his discussion of Larner's paper gives some curves of maxi- 
mum efficiencies attained by modern waterwheels of the Francis and 
tangential types. These curves slightly modified are reproduced in 
Fig. 295. 

The detailed design of a turbine and casing is mainly concerned with 
the angles of entrance and discharge of the vanes or buckets in the runner 
and of the direction of the entering water from the guide vanes. This 
is a highly specialized subject and beyond the scope of this book. Zowski 
in Engineering News, Jan. 6 and Feb. 10, 1910, gives perhaps the best 
treatment of this subject in English although Parker in his ''Control of 
Water" gives the treatment in good form. The general turbine equa- 
tion may be written : 

2gH = (t/2 - U^') + {W - W2') + {V - ¥2'). 

Where U and U2 are runner velocities, W and W2 are absolute velocities 
of the water and V and V2 are relative velocities of the water. This 
equation may be transformed into: 

2gH = AQ2 + BQn + Cn^ where H = head, Q = quantity of water, 
n = r.p.m. and A, B and C are coefiicients depending on bucket angles, 
friction and the proportions of the machine. This is also the general 
equation of the centrifugal pump with the signs changed: 

- 2gH = AQ^ - BQn - Cn\ 

This is the equation of a hyperbolic paraboloid. The analysis has 
been very carefully worked out by Grunebaum in his pamphlet, 
Zur Theorie der Zentrifugalpumpen, Berlin, 1905. W. F. Uhl in 
Transactions A.S.M.E., vol. 34, page 418, has published a variation of 
Gelpke's types, which is convenient to use. He uses six types instead 
of eight. 

The Holyoke Testing Flume. — The Holyoke testing flume grew out 
of the testing of waterwheels started by James Emerson at Lowell in 
the late sixties. In 1870 the Holyoke Water Co. invited Mr. Emerson 
to move to Holyoke and to establish a flume there. The present Holyoke 
flume built by Clemens Hersehell dates from 1883 and up to date more 
than 2,000 runners have been tested there. The flume is adapted for 
testing runners from 27 to 42 in. in diameter under a maximum head of 
about 16 to 17 ft. Capacities up to 250 cu. ft. per second may be used 
which reduces the available head to about 10 ft. Quantities higher than 
this cannot be measured with accuracy. 

The accuracy and application to general practice of the Holyoke 



560 ENGINEERING OF POWER PLANTS 

tests have been attacked very often, especially where a high-head turbine 
has been tested under the Holyoke conditions. 

However, at the present time these tests hold ''a position of gen- 
erally accepted reliability" and it is the opinion of many engineers 
that the results shown in the flume may be bettered in a careful 
field test (see Larner's paper). Testing in place is now quite common 
and when proper precautions are taken may be quite accurately 
done. 

The Holyoke test sheets usually contain 60 to 70 tests of 3 to 5 min. 
duration from which the following data is secured : number of experiment, 
percentage of gate opening, percentage of full discharge of wheel, head, 
duration of experiment, revolutions per minute, quantity of water dis- 
charged by wheel, horsepower developed, efficiency of wheel. 

From these data it is possible to construct a set of characteristic curves 
covering the whole field of the operation of the turbine. Mead has shown 
this in Fig. 295 and 247 of his ''Water Power Engineering.'^ Fig. 247 
is reproduced here. In this method the discharges per second under 
1-ft. head are used as abscissae with r.p.m. under 1-ft. head as ordinates. 
The efficiency under each gate opening and speed is plotted in its proper 
place with the above coordinates and the curves of equal efficiency are 
then drawn in. If hp. at 1-ft. head is now marked on each of the 
plotted points curves of equal horsepower may be drawn. From these 
curves the entire performance of the runner under all circumstances 
may be seen. 

Mechanical Details. — The standard wheel consists of two crowns 
between which the buckets are placed. The buckets are either made of 
formed steel plates placed in the molds and cast into the crowns or 
they may be made of the same material as the rest of the runner in which 
case the mold is built up with cores. Cast wheels are practically uni- 
versal now. No attempt at finishing is usually made except to chip or 
file off the fins left by the core junctions and some of the very highest 
efficiencies have been obtained from runners in this condition proving 
that surface friction does not play nearly as large a part as was formerly 
supposed. Careful design and good workmanship usually go together in 
which case much hand-finishing is not necessary. Balancing is not as 
necessary as in steam turbines but is done to some extent especially on 
tangential wheels where the buckets are usually of forged or cast steel 
bolted to the rim of the wheel. The larger diameter wheels are usually 
built on the tension-spoke principle. 

Clearances between fixed and moving parts in well-built wheels are 
not larger than J-fe iii-j although with careful design the water wasted 
through a clearance as large as ^^ in. would not be excessive when the 
wheel is running. When the wheel is not running the leakage is deter- 



HYDRAULIC POWER 561 

mined by the kind and tightness of the gates. It is always best to have 
a valve in the penstock just above the wheel so that when not in use the 
wheel may be drained and leakage prevented. For this purpose butter- 
fly valves of very heavy design, actuated by power have been found 
valuable but the best valve for high and medium heads is a plain gate 
valve actuated by a hydraulic cylinder. These valves should not be 
supposed to take the place of the stop logs or other headworks gates, but 
should be in addition to them. 

Casings. — The casings of water turbines may be of almost any form, 
and a good designer may display his individual taste to the full. With 
open penstocks the casing need only consist of the guides and the two 
narrow crowns holding them in place. With the closed penstock the 
scroll or spiral casing when well designed is the best. Cylindrical casings 
are used to a large extent especially when two or more wheels are on one 
shaft and when the casing supports the bearings in horizontal wheels. 
In designing casings the attempt should be made so to proportion the 
casing that at the loading at which the turbine is most often used the 
water will be brought to the guides at the required velocity without eddys 
and with a smooth stream flow. 

Draft Tubes. — Draft tubes should be so designed that there is a uni- 
form reduction of velocity from runner to tail water. The upper end of 
the draft tube should be the same diameter as the outside of the runner 
with a little flare at this point in the case of large-capacity runners to 
take care of the outward discharge from the buckets. From this point 
the tube should enlarge consistently to the discharge point and a flare 
of I ft. in diameter to 3 ft. in length is the maximum that may be allowed. 
One foot in 4 or 5 is much better. Knowing the height of the tube, the 
outlet is known and the loss of head can be calculated. This loss may 
vary from less than 1 per cent, of the total head to as much as 12 or 15 
per cent, in poorly designed installations. 

Gating. — Turbine gates for regulating the amount of water entering 
the runner are of three kinds: 

1. Cylinder gates in which a thin cylinder moves axially in the clear- 
ance space between guide vanes and runner blocking more or less of the 
breadth of the passages. This gate leads to eddys and inefficiency unless 
cross-partitions are cast between the vanes of the runner to control the 
formation of eddys (Fig. 308). 

2. Register gates in which the thin cylinder in the clearance space is 
perforated with holes to correspond to the guide passages and is moved 
circumferentially to control the size of the discharge openings in the guide 
passages. These gates are not used very much since they increase the 
friction and eddy losses seriously (Fig. 309). 

3. Wicket gates in which the guide vanes are pivoted and opened or 



562 



ENGINEERING OF POWER PLANTS 



closed to admit more or less water to the runner. This method also 
creates eddys at all positions but one, but they can be better controlled 
by this construction and wicket gates are adopted for the better class of 
turbines (see Fig. 310). 

Regulation. — The problem of waterwheel regulation is much more 
complicated than the regulation of gas or steam prime movers. The 





Fig. 308.— Cylinder gate. 



¥iG. 309. — Register gate. 



steam engine, with its two or more maximum impulses per revolution, 
presents a very simple problem, since a medium-weight flywheel can store 
enough energy from impulse to impulse to maintain a nearly uniform 
rotation until the cutoff or throttling governor can control the size of 
the next impulse. In a slow-moving single-cylinder engine the .flywheel 




Fig. 310.— Wicket or Fink gate. 

has only to store energy for ^{q sec. The regulating machinery is light 
in a throttling governor weighing only a few pounds, and a very small 
simple flyball governor furnishes sufl&cient power for quick and efficient 
working. 

With the steam turbine the same small and Hght machinery will do 
the work if a throttling governor is used. When nozzle governing or 



HYDRAULIC POWER 



563 



puff governing is used the relay principle is introduced. Here, as in the 
steam engine, the action is practically instantaneous and the flywheel 
effect of turbine and generator is always sufficient for good regulation. 

A single-cylinder, single-acting, four-cycle internal-combustion engine 
presents a much more difficult problem. With 75 r.p.m., the impulses 
are a little over 2 sec. apart and the loads can vary much in 2 sec. Four 
cylinders would bring the interval down to J^ sec. and four double- 
acting cylinders to J-^ sec, but in this case the mechanisms to be moved 
are large and heavy, as are the friction and inertia. It is possible to 
design a flyball governor having sufficient power to operate them, but 
the oil relay is easier, cheaper and more certain. 

In these types of prime hiovers the working fluid is very light even at 
high pressure and the inertia of the moving fluid is negligible, but when 

Time in Seconds 
4 5 6 




Fig. 311. — Regulation curves. 



dealing with water as a source of power the weight of the fluid is the 
source of energy and the governing mechanisms must be strong enough 
to take care of the heavy shocks due to the inertia of the moving water. 
The gate mechanisms of turbines are usually larger than the wheel itself 
and generally as heavy, while the connecting links are also very heavy. 
All of this heavy machinery cannot be put in motion, or stopped quickly, 
but luckily the flywheel effect of the revolving parts is usually large and 
the sudden impulses are not of the order of those in steam or gas engines. 
With small wheels and low heads a relay governor is used, but with 
higher heads or large wheels the relay does its work through a third 
mechanism, usually a rack and pinion. The usual arrangement includes 
a flyball governor which actuates two ratchets on a bar which is recipro- 
cated continually by the relay. When the speed rises, one of the ratchets 



564 



ENGINEERING OF POWER PLANTS 



is brought into play on the ratchet wheel and the reciprocating motion 
moves the wheel around, tooth by tooth, closing the gate. There is 
always a small speed variation at which no motion of the gate follows. 







Fig. 312.— Waterwheel governor, Sanitary District of Chicago. 

In this kind of a governor there is always a lag and the length of lag 
is adjusted to take care of some of the inertia of the water column. 
Much trouble in the earlier governors was caused by the attempt to run 




Bronze 
Button 




Fig. 313. — Step bearings. 



Fig. 314. — Step bearings. 



them without lag and trouble also results if the lag is too much. The 
correct amount seems to depend on head, revolutions, size of penstock 
and weight of gate mechanism. 

Two general principles may be stated : first, the gate must be opened 



HYDRAULIC POWER 



565 



only as fast as gravity can supply the water to the wheel; and second, 
the gates must be closed so slowly that no serious strains will be devel- 
oped in the penstock from the inertia of the water. Wherever it is 
pK)ssible, the gate mechanism should be in static balance, except as to 
friction. This is not always possible, but it can be partially done in every 
case and the governor is then relieved of work which it should not be 
called upon to do. Fig. 311 shows the curves of opening and closing of 
a modern type of governor, and Figs. 312 and 315 show the governors 




Fig. 315. — Waterwheel governor. 

and the relay mechanism. For parallel running of waterwheels and steam 
or gas engines it is essential that ^the flyball governors of the machines 
have the same characteristics, although there are modifying influences, 
such as flywheel action. The difficulty of dividing the load between 
water and steam units has been largely overcome, and with the modern 
governors the troubles experienced are small. 

Practically the only auxiliaries of a waterwheel, besides the governor 
are the thrust bearing and oiling system, and on the horizontal shaft 



566 



ENGINEERING OF POWER PLANTS 



turbines thrust bearings are usually not required. For small wheels the 
old lignum vitse step bearing or phosphor-bronze button, run with water 
lubrication, is still the best construction, see Figs. 313, 314, but shafts 
larger than 5 in. and very fast-running shafts do not work well unless the 
design is ample. In the larger modern designs the thrust bearing is 
placed near the top of the shaft below the generator, where it may be 
supported from the floor framing, or with the later Kingsbury thrust the 
bearing is placed above the generator on the spider which supports the 
upper bearing. The older thrusts consist of two cast-iron surfaces, face 
to face, the lower one fixed and the upper revolving with the shaft. To 
the center of pressure of these surfaces oil or water is piped under sufficient 




Fig. 316. — Kingsbury thrust bearing. 



pressure to raise the shaft one or two-thousandths of an inch. The oil 
or water escapes through the orifice and the upper shoe will run on the 
film of fluid so made. In the Kingsbury bearing the revolving surface 
is replaced by a number of smaller rectangular shoes, supported at a 
point behind the center of pressure. These shoes are babbeted on the 
face side and scraped to a true surface, but the forward edges are eased 
to allow the oil to enter under them. The lower shoe is covered with 
about 3 in. of oil which may be circulat^d to keep it cool. These bearings 
are shown in Fig. 316 and Fig. 317 shows the oil-pressure bearing for the 
same weight, such as was used at Niagara Falls. Where the pressure 
bearing is used a rather complicated oil- or water-supply system is neces- 
-sary and pressures up to 700 or 800 lb. per square inch are often used. 



HYDRAULIC POWER 



567 



The oiling systems are usually gravity systems, provided with a sump 
for the dirty oil, from which it is pumped through filters to supply tanks 
near the roof of the station. If the head necessary to work the governor 
relays is higher than the gravity head in the station, two small pumps 
and an accumulator are usually installed for this purpose. On horizontal- 
shaft machines of small size, ring oiling bearings are usually used, but 
lignum vitse bearings with water lubrication are also common. For the 
larger horizontal shaft turbines the regular gravity oiling system should 
be installed. Flood lubrication, with higher bearing pressures, surface 
speeds and oil temperatures are the tendency at the present time. 




Oil Catcher 

Fig. 317. — Oil-pressure thrust bearing. Niagara Falls Power Co. 

Head Races, Canals and Flumes. — It is frequently necessary in 
order to take advantage of the total fall, to place the dam at the narrowest 
portion of the stream where good foundations are available and locate 
the power house a considerable distance down stream bringing the water 
to the power house in open channels, such as head races, earth or rock 
canals, or tunnels or pipe lines. Wooden flumes of rectangular section 
were formerly used for small powers or in localities where lumber was 
very cheap. The sides and bottom were usually made of two thicknesses 
of planking with broken joints. The deterioration in these flumes was 
very rapid. 



568 



ENGINEERING OF POWER PLANTS 



When the canal is in earth or rock it usually pays to line it with con- 
crete. A velocity of 2 ft. per second may be allowed in unlined earth 
canals and 8 ft. per second in lined canals. It is not unusual to find these 

canals exceeding 6,000 ft. in length. In all 
cases the head lost in the canal must be more 
than made up by the lower location of the 
power house. 

From both canals and flumes penstocks 
of wood or metal must be used to convey 
the water to the wheels or the canal or flume 
may be replaced by metal or wood stave pipe. 
The local configuration of the country usually 
determines which is the better plan to be 
used. If th'e stream is terraced, the canal 
may be the much better method. 

If rock ridges exist between the dam and 
the proposed power house site with a wind- 
ing stream and broken country, pressure 
tunnels in the solid rock have been driven in a 
straight line to the wheels, thus saving much 
distance and consequent loss of head. Water 
from a dam in one watershed has been taken 
in a tunnel under the ridges to the adjoining 
watershed and utilized to better advantage 
there. The lining of these tunnels should be 
very smooth. Very good results are obtained 
from this construction. The reports of the 
Board of Water Supply of the City of New 
York contain much interesting information, 
but the best data on these tunnels is to be 
found in the report on the Hetch-Hetchy 
Water Supply for San Francisco by John R. 
Freeman, Past President, A.S.M.E. This 
report is a model of its kind and will repay 
careful study by the engineer. 

For figuring the slope and loss of head in 
canals, flumes and tunnels the tables given 
in Williams and Hazens ''Hydraulic Tables" 
(Wiley) are most convenient. 

Wood pipe should not be painted but, 

for a good length of life, should be protected 

by a house or covered with earth although the latter has the disadvantage 

that the pipe cannot be inspected. Steel pipe is protected by the Angus 




HYDRAULIC POWER 569 

Smith covering and either buried or unprotected. All pipes should have a 
large air vent near the intake end to prevent collapsing when the water 
is drawn off and on long pipes additional vents are often installed. Air 
valves should be placed on high points. The plant at Salmon Falls, 
N. Y., illustrated in Fig. 318, is a good example of the use of tunnel, 
wood pipe and steel pipe. 

Water Tower or Standpipe. — If an open penstock is possible, this 
form of construction will undoubtedly be the best as fluctuations of head 
or pressure due to inertia will be very small indeed. With canal con- 
struction and low heads the .surplus water can easily be taken care of by 
a small spillway. When closed penstocks of any length are necessary, 
the inertia of the moving water, as its velocity fluctuates due to the 
governing of the wheels to meet changes of load, may create dangerous 
pressures or surges. In a small installation at low head or even up to 
200 ft. it has been usual to place a standpipe as close to the turbines as 
possible with its height great enough to reach above the dam level. In 
addition to this spring loaded relief valves are always furnished at the 
end of the penstock to further relieve the undue rise in head. The 
water tower may be of the plain cylindrical type as at Trenton Falls 
or the two diameter or differential type as at Salmon Falls (Fig. 318). 
They may be built of steel or reinforced concrete up to 200 ft. high, 
but usually the cheaper and stronger construction is steel above 
100 ft. high. 

A valuable chapter on the design and use of the water tower may be 
found in D. W. Mead's "Water Power Engineering" and a discussion 
of the formulas and methods of design in Parker's ''Control of Water." 

Speeds of Turbine and Generator. — In most cases hydro-develop- 
ments are utilized by means of electric generation and transmission and 
it becomes important to place the r.p.m. of the turbine at such a figure 
that the electric generator will be reasonably cheap and suited to the serv- 
ice. Francis wheels may be built for many permissible speeds, in 
fact for any horse-power and head combination the range of speeds is 
very large. Table A has been calculated for C = 90 to C = 10 and 
for heads from 100 to 600 ft. giving minimum and maximum speed 
values 'for a number of generators from 200 kw. to 10,000 kw. 

The figures under C = 10 are the lower speed limits for that head, 
under C = 90 the higher Umits. It is well not to approach either limit 
too closely. 

Most of the hydro-systems in this country have been designed to 

use 60-cycle current but a few plants have been built using 40 cycles and 

a considerable number using 25 cycles. In Europe other frequencies are 

sometimes used. Table B gives the speeds of 60-, 40- and 25-cycle 

2 X 60 X cvcles 
generator, with common pole numbers. j — '- = r.p.m. 

3Q 



570 



ENGINEERING OF POWER PLANTS 
Table A. — Possible Revolutions Per Minute 







C 




10 90 10 90 10 90 


10 


90 


10 90 


10 90 


Kw 


Hp. 














Head 




100-ft. 


200 ft. 


300 ft. 


400 ft. 


500 ft. 


600 ft. 


10,000 


13,800 


27 


243 


63 


567 


106 


954 


152 


1,368 


202 


1,818 


253 


2,277 


5,000 


6,900 


38 


342 


90 


810 


150 


1,350 


215 


1,935 


282 


2,538 


358 


3,222 


2,000 


2,760 


61 


549 


143 


1,287 


237 


2,133 


341 


3,069 


450 


4,050 


566 


5,094 


1,000 


1,380 


85 


765 


202 


1,818 


335 


3,015 


480 


4,320 


635 


5,715 


798 


7,182 


500 


690 


121 


1,089 


286 


2,574 


474 


4,266 


680 


6,120 


900 


8,100 


1,130 


10,170 


300 


413 


157 


1,413 


370 


3,330 


614 


5,526 


882 


7,938 


1,164 


10,476 


1,464 


13,176 


200 


276 


182 


1,638 


453 


4,077 


750 


6,750 


1,078 


9,702 


1,425 


12,825 


1,790 


16,110 













Table B.— R.P.M. 




















Poles 


2 


4 


6 


8 


10 


12 


14 


16 


18 


20 


22 24 


26 28 


30 


32 


36 


40 


72 


60 cycles 

40 cycles 

25 cycles 


3,600 
2,400 
1,500 


1,800 

1,200 

750 


1,200 
800 
500 


900 
600 
375 


720 
480 
300 


600 
400 
250 


514 
343 
214 


450.0 
300.0 
187.5 


400 
367 
167 


360 
240 
150 


327 
218 
136 


300 
200 
125 


277.0 
185.0 
115.5 


257 
172 
107 


240 
160 
100 


225 

150 

94 


200 
184 
84 


180 

120 

75 


100 
92 

42 



Of Francis wheels from 200 kw. to 10,000 kw. installed in the last few 
years on heads up to 600 ft. the r.p.m. have varied from about 94 to 514, 
these being the limits in which the cost of the generator- has balanced 
against the turbine cost. Six hundred r.p.m. seems to be a favorite 
speed for both small and large units of the tangential type but speeds as 
high as 900 and as low as 200 have been used. 

In many cases the spacing of the units and design of the headworks 
settle the permissible diameters and speeds. 

Cost of Hydraulic Installations. The total cost of a hydraulic instal- 
lation may be divided into two parts: first, the dam, land damages, 
spillway, canals, flumes, pipe lines or penstocks and other details relating 
to the storage and transportation of the water; and second, the power 
house, turbines and electrical apparatus. The first group will usually 
amount to 50 per cent, of the total cost in small low-head plants, rising 
to 65, 70 and sometimes 80 per cent, in large high-head installations. 
Where a large amount of storage is constructed the storage itself may in 
large plants amount to 50 per cent, of the total cost. 

The installation cost per kilowatt varies greatly, depending on local 
conditions, from $50 per kilowatt, where the best conditions prevail, 
to as high as $300 or more, where the conditions are not good. It is 
usually considered that a cost of $125 per kilowatt represents the limit 
of economical construction, with interest at 6 per cent. Where the 
capitalist will put up with a smaller return than 6 per cent., higher-cost 



HYDRAULIC POWER 



571 



plants may be possible. Not infrequently unknown physical con- 
ditions largely increase the cost of installation of a water power. 
When this occurs the project usually goes into a receiver's hands and 
enough capital is written off so that the work may proceed. In a number 
of cases this accounts for the very low reported costs of certain plants. 

The construction of the dam is largely a matter of excavation and 
masonry or concrete. Earth excavation may be figured as low as 25 cts. 




Fig. 319. — Section through 17,500 turbine unit Coosa River, Lock 12 development. 



per cubic yard under good conditions, but where much hauling has to be 
done or difficult conditions must be met, prices as high as $1 to $1.25 must 
be used. Rock excavation is rarely cheaper than $1 per cubic yard under 
the best conditions, and may go to $3 in bad locations and as high as 
$10 to $15 in caisson work. Concrete and masonry can easily be figured 
when the prices of sand, cement and rock are known. Concrete usually 
runs from $4.50 to $10 per yard in place, $5.50 to $7 is about the average 
where concrete can be placed in mass and the forms are simple. The 



572 



ENGINEERING OF POWER PLANTS 




HYDRAULIC POWER 573 

local price of lumber determines the cost of the forms which will rarely 
be higher than $2 per yard, in which case steel forms should be con- 
sidered. Lumber delivered at S40 or higher usually means that con- 
siderable steel may, with economy, be used in the forms. Cut-stone work 
may run from $12 to $25 per yard, but is very rarely used in commercial 
construction at the present day. Power houses and switch and trans- 
former houses should be figured as in steam plants. The steel contract 
will average from 8 cts. per cubic foot in small buildings to 16 cts. per 
cubic foot in large heavy buildings, all on the basis of $80 per ton erected. 
The masonry contract will run from 12 cts. to 30 cts. per cubic foot de- 
pending on locality, materials and amount of terra cotta, tile and cut 
stone and other ornaments. 

Hydraulic machinery and governors vary in price with head and size; 
small low-head turbines cost approximately $15 per kilowatt, while 
large low-head machines may be bought as low as $7. Medium-head 
apparatus (from 200 to 600 ft.) may vary from $13 to $7.50 per kilo- 
watt. High-head turbines of the Pelt'on type run from $10 per kilowatt 
in small sizes down to $5 in large sizes. Generators, switchboard, 
exciters and cable vary from $24 per kilowatt for small low-head (low- 
speed apparatus) to $8 per kilowatt for large high-head high-speed 
machinery. Transformers cost $6 to $8 per kilowatt. 

Penstocks or pressure pipes of riveted steel vary in cost from 3 cts. 
to 6 cts. per pound erected, plus freight and haulage. Wood stave pipe, 
used to such a large extent for low-head pressure pipes, will cost about 
15 cts. per foot board measure, erected, with bands, for medium sizes 
and pressures. 

Gates of the Taintor type will not usually run above 5 cts. a pound 
erected, plus freight and haulage. Stoney gates in small sizes may run 
to 8 cts., but in the large sizes should not exceed 5 cts. Cranes for use 
inside the power station of both the alternating-current and direct-cur- 
rent types, may be figured at $4.50 per ton hfted per foot of span for 
small short-span cranes, down to $2.50 per ton-foot for heavy long-span 
cranes. Special cranes, used outside the power house for handling gates, 
may cost anywhere from $3 to $10 per ton-foot, depending on the design. 

The question of land damages, due to flooding caused by the creation 
of the pond, is an extremely important one. This cost in certain plants 
in the West, where the flooded lands were far from a settled district, have 
been as low as $1 per acre, while in certain of the large city water-supply 
reservoirs, the land damages amounted to over $250 per acre. On an 
average for developments reasonably removed from towns, prices from 
$70 to $115 per acre have been paid. 

Railroads and highways usually follow rather closely the flow line of 
a river, and these constructions must be relocated previous to the con- 



574 



ENGINEERING OF POWER PLANTS 



struction of the dam. $3,000 per mile is a fair price for country highway 
relocation and from $5,000 to $8,000 per mile will cover the relocating 
of a good State road in localities where good materials are common. 
The cost of railroad relocation is another matter. Single-track little- 
used roads may usually be relocated at a cost not exceeding $60,000 a 
mile, but the cost of relocating a double-track express road has usually 
been found so high that it has not been attempted. 

Table of Estimated Cost per Horsepower of Water-power Plants 

Having horizontal turbines, steel penstocks, and walled tailraces (dam and 

buildings not included) 



Hp. 


"L" 


10 ft. fall 


15 ft. fall 


20 ft. fall 


30 ft. fall 


40 ft. fall 


1,000 


f 100 


$65.14 


$40.92 


$29.37 


$19.40 


$14.60 




\ 600 


98.75 


63.75 


46.70 


30.95 


23.55 


900 


1 100 


65.35 


41.00 


29.55 


19.55 


14.80 




\ 600 


98.95 


63.90 


46.95 


31.00 


23.85 


800 


f 100 


65.50 


41.10 


29.65 


19.70 


15.00 




\ 600 


99.15 


64.00 


47.00 


31.15 


23.95 


700 


1 100 


65.70 


41.20 


29.85 


19.90 


15.10 




\ 600 


99.50 


63.95 


47.25 


31.35 


24.15 . 


600 


1 100 


65.85 


41.55 


30.00 


20.00 


15.35 




\ 600 


100.10 


64.40 


47.40 


31.80 


24.55 


500 


/ 100 


66.00 


41.70 


30.25 


20.25 


15.50 




\ 600 


100.10 


64.00 


47.85 


31.80 


24.45 


400 


100 


66.30 


42.05 


30.55 


20.80 


16.00 




1 600 


100.00 


65.15 


48.05 


32.35 


25.10 


300 


/ 100 


66.85 


42.65 


31.10 


21.50 


16.50 




\ 600 


101.00 


65.80 


48.50 


33.20 


25.65 


200 


100 


68.50 


44.20 


32.45 


22.60 


17.60 




\ 600 


102.85 


67.35 


50.60 


34.45 


26.95 


100 


/ 100 


71.40 


46.65 


34.75 


24.75 


19.80 




\ 600 


106.60 


70.30 


52.90 


36.85 


30.80 



"L" = distance from feeder head to end of tailrace, cost of canal, if any, not 
included. 

Cost of Hydro -electric Developments. — The cost of hydro-electric 
developments depends upon many conditions, such as water rights, real 
estate, right-of-way, the cost of the development, and the distribution 
system. Further, the depreciation, repairs, taxes, insurance, interest 
on the investment, operating expenses, etc., enter into the account. 

The cost of the enterprise depends very much on the character and 
the conditions under which the development is carried out, and the cost 
per unit capacity depends upon the total capacity of the plant. It 
occurs quite frequently that the unit cost in large propositions is greater 
than in small ones, although it would appear that it should be smaller. 



HYDRAULIC POWER 



575 



Table I. — Estimate of Cost of Various Developments 



Location of development 



Natural 
head 



Available L P^^^^, 
head deve^loped. 



Estimated 

capital 

cost 



Cost 
per 
hp. 



Healey's Falls, Lower Trent River . . . 
Middle Falls, Lower Trent River . . . 

Rauney's Fall 

Rapids above Glen Miller 

Rapids above Trenton 

Maitland River^ 

Sangeen River ^. . . 

Beaver River (Eugenia Falls) 

Severn River (Big Chute) ^ 

South River •. . 

St. Lawrence River, Iroquois, Ont . . . 
Mississippi River, High Falls, "A"^. 
Mississippi River, High Falls, "B"^. 
Montreal River, Fountain Falls, Ont. 

Dog Lake, Kaministiquia River^ 



Cameron Rapids. 
Slate Falls 





60 


8,000 




30 


5,200 




35 


6,000 




18 


3,200 




18 


3,200 




80 


1,600 




40 


1,333 




420 


2,267 




52 


4,000 




85 


750 




12 


1,200 




78 


2,400 




78 


1,100 




27 


2,400 




547 310 


13,676 




547 310 


6,840 




39 


16,350 




39 


8,250 


{ 


31 40 


3,686 


31 40 


1,843 



$675,000 
475,000 
425,000 
350,000 
370,000 
325,000 
250,000 
291,000 
350,000 
150,000 
179,000 
195,000 
123,000 
214,000 
832,000 
619,700 
815,000 
600,000 
357,600 
260,000 



$84.38 

91.37 

69.67 

109.38 

115.63 

203.12 

187.53 

128.28 

87.50 

153.33 

149.16 

81 

181 



61 
91 



50.00 

73.00 

97.00 

141.00 



1 Dam rather expensive. ^ Head works and canal less expensive than ordinary. 
' With storage development. ^ Including 3,500 ft. of head water tunnel. 



Table IL — Estimate of Cost of Hydro-electric Plants at Niagara Falls 





24-hr. power capacity 




50,000-hp. 
development 


75,000-hp. 
development 


100,000-hp. 
development 


Tunnel tailraces 


$1,250,000 
450,000 
500,000 
300,000 
1,080,000 
760,000 
350,000 
100,000 
75,000 


$1,250,000 
450,000 
700,000 
450,000 
144,000 
910,000 
525,000 
100,000 
75,000 


$1,250,000 
450,000 


Headworks and canal 


Wheel pit 


700,000 


Power house 


600,000 


Hydraulic equipment 


1,980,000 
1,400,000 


Electrical equipment 


Transformer station and equipment . 
Office building and machine shop . . . 
Miscellaneous 


700,000 

100,000 

75,000 






Engineering and misc. 10 per cent, of 
above making total construction 
cost 


$4,865,000 

$5,350,000 
436,560 


$5,900,000 

$6,490,000 
529,548 


$7,255,000 
$7,980,000 


Interest, 2 years at 4 per cent 


651,168 


Total capital cost 


$5,786,560 
$114 


$7,019,584 
$94 


$8,631,168 


Per horsepower 


$86 







576 ENGINEERING OF POWER PLANTS 

This is due to the fact that in many large propositions a heavy expense is 
involved in the harnessing of great volumes of water. 

Table I, accompanying, gives figures on the estimated costs of various 
developments tabulated by the Ontario Hydro-electric Power Commis- 
sion, and Table II gives the estimated cost of a hydro-electric plant at 
Niagara Falls, as given in the report of above-named Commission. 

It will be noticed by reference to Table I that the cost of hydro- 
electric plants per horsepower, varies greatly (from $61 to $203) and may 
vary even more. Correct estimates can be arrived at only by thorough 
investigation of all the factors, considering with especial care the impor- 
tant element of depreciation. 

In estimating the cost of power (that is, the generation and dis- 
tribution, which of course depends very much upon the load factor) 
administration and operating expense, maintenance, depreciation, inter- 
est, insurance, etc., must also be well considered. The following table 
clearly illustrates the cost of power at the development of the Chicago 
Sanitary District System. 

Table III. — Cost of Power, Chicago Sanitary District System 
Total cost of development and transmission $3,500,000 

Estimates of cost 

Interest on investment at 4 per cent $140,000 . 00 

Taxes on real estate, buildings, etc 7,200,00 

Depreciation on buildings at 1 per cent 3,650.00 

Depreciation on waterwheels at 2 per cent. . 2,027.32 

Depreciation on generators at 2 per cent 1,824.60 

Depreciation on pole lines at 3 per cent 2,020. 50 

Depreciation on other electrical appliances at 3 per 

cent 3,995.52 

Total fixed charge ^ 161,137.94 

Operating expenses 

Power and substation labor $63,240 . 00 

Repairs to machinery and building 3,700.00 

Incidental expenses ; 1,200 . 00 

Operating Lawrence Avenue pumping station 43,960.00 

Operating 39th Avenue pumping station 120,380.00 

Interest on investment 39th Street pumping station . . 15,599 . 76 

Total operating expense 248,079. 76 

Total cost to sanitary district '. $409,217 . 76 

Capacity, 15,000 hp., cost per hp. per annum 26 . 40 

A most important item in determining the cost of power is the cost 
of distribution. This is particularly true in long-distance transmission 



' 



HYDRAULIC POWER 577 

systems where the skill of the engineer is of vital importance in selecting 
the proper route and the kind of systems to be employed. 

Whether a long-distance power-transmission project will pay will 
depend upon the cost of generating the power, the cost of transmission, 
the transmission loss, etc., and the value of energy at the point of dis- 
tribution, i.e., the cost at which energy might be generated at this point 
by some other system, as, for instance, by a steam power plant. The 
difference between the cost of power at the generating end and its value 
at the point of distribution represents the maximum cost of transmission 
allowable. 



INDEX 



Actual fuel consumption and cost of oper- 
ation of existing plants, 509 
Advantages and disadvantages o^ various 

fuels and of electricity, 399 
Advantages, engine, 71 

of revolving-grate producers, 472 
of the internal-combustion principle, 
418 
Advantages, turbine, 71 
Air, compressed, 519 

compressor cylinders, oil in, 527 
compressors, volumetric efficiency 

of, 526 
condensers, 96 
-lift pump, 525 

-pump system, the kinetic, 108 
pumps, steam jet, 109 
system at Butte and Anaconda, com- 
pressed, 528 
Alcohol and gasoline, comparative re- 
sults from denatured, 414 
Alignment, 86a 

Alternating current, direct current vs., 
327 
motors, 329 
Alternators, exciters for, 332 
Amount of fuel used by producer-gas 

power plants, 461 
Anacaonda, compressed-air system at 

Butte and, 528 
Analysis of development in a power plant, 

16 
Animal motors, 4 

Animals, muscular power of men and, 2 
Annual cost of power, 309 
Anthracite, 366 

Apparatus for turbines, condensing, 95 
Apparent power, kilovolt amperes, 332 
Applicability of engines, 71 

of turbines, 71 
Arrangement of the power plant, 242 
Ash handling, 236 
coal and, 232 



Ash handling, cost of, 237 

Aspects of the turbine, commercial, 70 

Auxiliaries, boiler, 1966 

condenser, 99 
Auxiliaries, percentage of steam gener- 
ated used by, 208 
power required by producer, 467 
Auxiliary steam piping, 218, 222 , 
Auxiliaries, steam used by, 208 
Average cost of boilers, 138 

of stacks and flues, 178 
heat balance for test locomotive, 363 
steam consumption of reciprocating 
steam engines, 51 
Axis, engines classified by position of 
cylinder, 20 



B 



Bagass, 372 

Bark, tan, 372 

Basic principles of steam turbines, 39 

Beam engines, 21 

Belting, cost of shafting and, 320 

electric drive vs. shafting and, 321 
shafting and, 320 
Bituminous coals, 367, 377, 460 

semi-, 367 
Blast furnace as a gas producer, the, 491 
-furnace gas-electric plants, cost of, 
493 
power, cost of, 493 
gas power, cost of steam and, 507 
Bleeder and mixed pressure turbines, 

low-pressure, 46 
Blowing engines, piston compressors and, 

520 
Blowers, soot, 214 
Boiler and furnace efficiency, 158 
Boiler auxiliaries, 1966 

capacity required by office buildings, 

estimating, 348 
construction, specifications for, 128 
deterioration, 163 
efficiency, 158 



579 



580 



INDEX 



Boiler efficiency, with oil fuel, 395 

explosions, 163a 

feed water, 210 

inspection, 163a 

materials, 126 

performance, locomotive, 359 

plant operation, principal losses in, 
165 
Boiler pressure, maximum, 128 

rating, 158 

returns, high-pressure drip piping 
and, 223 

-room piping details, 221 

settings, 130 

the steam, 121 

types, dependability of the different, 
126 
selection of, 163b 
Boilers, average cost of, 138 

cost of fire-tube, 134 
water-tube, 135 

cylindrical-flue, 122, 124 

hanging or supporting, 133 

horsepower rating of, 130 

idle, 163 

natural gas under steam, 397 

oil vs. coal under, 392 

operation and care of, 165 

return-tubular, 122, 125 

space required by, 139 

to do given work, number of, 163b 

types of, 121 

water-tube, 123, 125 

weight of, 139 
Bolts, 218 

foundation, 86 
Brick chimneys, cost of, 177 
Briquets, fuel 374 

in torpedo-boat service, 382 

results of experiments with, 381 

use of, 381 
Buck-stays and tie-rods, 132 
Building, the power plant of the tall 

office, 347 
Buildings, cost of, 247 

division of the load in tall office, 
347 

estimating boiler capacity required 
by office, 348 
miscellaneous steam requirements 
in large, 341 



Buildings, refrigeration for office, 350 

selection of plant for tall office, 347 
Burners, oil, 209 
Butte and Anaconda, compressed-air 

system at, 528 
Buying coal, when, 375 
Byproducts and smoke reduction, coal, 

196a 
Byproduct coke-oven gas plants, 489 
heating plant, the 334 
producer-gas plants, 482 

operating results- and working 
costs of, 486 



Canals and flumes, head races, 567 
Capacity of fans and power required, 
181 

of windmills, 8 

required in exciters, 332 
Care of boilers, operation and, 165 
Carrying peak loads economically, 28S 
"Cascade control" methods, 330 
Casings of water turbines, 561 
Central station design, 276 

heating and power, comparative costs 
of private and, 351 

power, isolated plants vs., 496 
Centrifugal feed pumps, 197 
Chain grates, 151 
Charcoal, 373 
Chimney dimensions, 176 
Chimneys, 166 

and mechanical draft, 166 

cost of brick, 177 
special, 178 
Circulating pumps, 99 

water, 416 
Classification of engines by their use of 
steam, 22 
special, 34 

of turbines, 40 
Cleaning the gas generator, 466 
Coal and ash handling, 232 

byproducts and smoke reduction, 
196a 

factors affecting value of, 376 

handling, 232 

in steam power plants, saving, 496 
cost of, 235 



INDEX 



581 



Coal per square foot of grate area per 
hour, pounds of, 163 
pounds of water evaporated per 

pound of dry, 162 
specification standards for purchase 

of, 377 
storage, 237 
the purchase of, under specifications, 

375 
under boilers, oil vs., 392 
when buying, 375 
Coals, bituminous, 367, 377, 460 , 

semi-bituminous, 367 
Coke, 373 

Coke-oven gas plants, byproduct 489 
Cold storage, 536 

Combined engine and turbine, economy 
of, 60 
unit, 48 
Combustion, 153 

Combustion engines, horsepower of in- 
ternal, 406 
internal, 402 

lubrication of internal, 417 
pressures and temperatures in 
internal, 415 
Commercial aspects of the turbine, 70 
Commutating-pole motors, interpole or 

329 
Comparative cost of operating different 
types of power installations, 
examples of, 503 
costs of private and central station 

heating and power, 351 
cost of steam power stations, com- 
plete, 250 
efficiencies and operating costs for 
different types of installations, 
496 
results from denatured alcohol and 
gasoline, 414 
Comparison of steam turbine with steam 

engine, 40 
Composition of producer gas, 439, 463 
Compound and multiple-expansion en- 
gines, 31 
condensing Corliss engines, cost of, 67 
engines, cost of, 69 
Compressed air, 519 

-air system at Butte and Anaconda, 
528 



Compressor cylinders, oil in air, 527 
Compressor, and blowing engines, piston, 
520 
volumetric efficiency of air, 526 
Concrete foundations, cost of, 84 
Condensate pumps, 100 
Condensation, mixed, 87 

surface, 90 
Condenser auxiliaries, 99 

installations, cost of individual, 116 
pumps, power required for, 113 
Condensers, 87 
air, 96 
cost of, 114 
evaporative, 97 
formulae for cost of, 116 
Condensing and non-condensing engines, 
27 
apparatus for turbines, 95 
Corliss engines, cost of compound, 67 
Condensing engines, cost of compound, 69 
probable gain in steam consumption 
by, 52 
Conditions, special producer-gas engine, 

458 
Conservation, reliability and, 496 
Construction, specifications for boiler, 

128 
Constructions, power plant, 239 
Consumption by condensing, probable 
gain in, 52 

of feed pumps, steam, 196b 
of reciprocating steam engines, aver- 
age steam, 51 
of small steam turbines, steam, 58 
variable-load steam, 61 
Conversion of tarry vapors into fixed 

gases, 451 
Cooling ponds, 116 
towers, 117 
cost of, 119 
Corliss engines, cost of compound con- 
densing, 67 
cost of simple non-condensing, 64 
Corrosion, 213 
Cost curves at variable loads, 302 

of a horsepower at the machine, 326 
of ash handhng, 237 
of blast-furnace gas electric plants, 
493 
power, 493 



582 



INDEX 



Cost of boilers, average, 138 

of brick chimneys, 177 

of buildings, 247 

of byproduct producer-gas plants, 
operating results and working, 
486 

of coal handling, 235 

of compound condensing Corliss 
engines, 67 
condensing engines, 69 

of concrete foundations, 84 

of condensers, 114 
formulae for, 116 

of cooling towers, 119 

of Diesel engines, 432 

of electric generators and motors, 
efficiency and, 77 
power in New York City, the, 299 

of energy in fuels, 399 

of exhaust steam heating, 339 

of feed pumps, 199 

of feed-water heaters, 203 

of fire-tube boilers, 134 

of fuel with different types of instal- 
lations, relative, 500 

of gas engines, 422 
Cost of gas producers, 476 

of hydraulic installations, 570 

of guyed iron stacks, 177 

of hydraulic installations, 570 

of hydro-electric developments, 574 

of individual condenser installations, 
116 

of injectors, 201 

of installations complete, 248 

of mechanical stokers, 164 

of oil, waste and supplies, 263 

of operating different types of power 
installations, examples of com- 
parative, 503 

of operation of existing plants, actual 
fuel consumption and, 509 

of piping, 228 

of power, 285 
annual, 309 

of producer-gas installations, 477 
power plants, operating, 479 

of shafting and belting, 320 

of simple, high-speed engines, 63 
non-condensing Corliss engines, 64 

of special chimneys, 178 



Cost of stacks and flues, average, 178 
of steam and blast-furnace gas 
power, 507 
and producer-gas plants, relative, 
478 
of steam engines and steam turbines, 

efficiency, economy and, 49 
of steam power stations complete, 

comparative, 250 
of steam turbines, 69 
of water, 120, 264 
of water-tube boilers, 135 
station, 256 
fuel, 256 
labor, 259 
maintenance, 263 
vs. economy of operation, first, 74 
Costs for different types of installations, 
comparative efficiencies and 
operating, 496 
of private and central station heat- 
ing and power, comparative, 351 
Coverings, pipe, 228 

Cubic feet of gas per pound of fuel, 465 
Current, rated, 332 
Curves at variable loads, cost, 302 

load, 301 
Cut-off engines, throttling and, 32 
Cylinder axis, engines classified by posi- 
tion of, 20 
Cylinder, horsepower of a, 18 
Cylindrical-flue boilers, 122, 124 

D 

Dams, 537 

Data on Diesel engines, summary of 

general, 432 
Denatured alcohol and gasoline, com- 
parative results from, 414 
Dependability of the different boiler 

types, 126 
Depreciation, 253 

and maintenance of stacks and 
mechanical draft systems, 184 
of locomotives, 358 
Design and proportions of turbines and 
runners, 555 
central station, 276 
furnace, 140 
of power plant, 239 
types of station, 244 






INDEX 



583 



Details of water turbines, mechanical, 

560 
Deterioration, boiler, 163 
Determining pipe sizes, 225 
Development in a power plant, analysis 
of, 16 
of the gas engine, rapid, 419 
Diesel engines, cost of, 432 

summary of general data on, 432 
Difference between steam and water 

turbines, 39 
Different boiler types, dependability of 
the, 126 
types of installations, comparative 
efficiencies and operating costs 
for, 496 
relative cost of fuel with 500 
of power installations, examples 
of comparative cost of operat- 
ing, 503 
Dimensions, chimney, 176 
of gas producers, 476 
Direct-current motors, types and where 

used, 328 
Direct current vs. alternating current, 

327 
Disadvantages of the internal-combus- 
tion principle, 419 
of the various fuels and of electricity, 

advantages and, 399 
of various pipe systems, 219 
Distribution, gas, 490 
District heating, 334 
Diversity factor, 274 
Division of the load in tall office build- 
ings, 347 
Domestic heating, natural gas for, 398 
Double-acting engines, single- and, 24 

-zone producer, the, 455 
Down-draft producer-gas plant, opera- 
tion of a typical, 449 
producer, the, 449 
Draft, chimneys and mechanical, 166 
forced and induced, 179 
systems, depreciation and mainte- 
nance of stacks and mechanical 
184 
efficiency with stack and mecha- 
nical, 185 
tubes, 561 
Drawbar pull of the locomotive, 356 



Drawing fires, time between periods of, 467 

Drip piping and boiler returns, high- 
pressure, 223 

Driving, rope, 320 

Dry coal, pounds of water evaporated 
per pound of, 162 

Dulong's formula, 369 

Duty of pumping engines, 61 



E 



Eccentric-grate gas producer, revolving, 

471 
Economizers, 204 

Economy of combined engine and tur- 
bine, 60 
of gas engines, thermal efficiency 

and, 412 
of operation, first cost vs., 74 
of windmills, 9 
steam engine, 51 
tests of steam engines, 54 

of turbines, 58 
variable load, 269 

with increase of steam pressure in 
the locomotive, increased, 357 
Effect of speed on average steam pres- 
sure, 357 
Effects of semi and totally enclosing 
direct-current motors, 333 
of smoke, 192 
Efficiencies and operating costs for differ- 
ent types of installations, com- 
parative, 496 
of different types of engines, thermal, 

499 
thermodynamic, 25 
Efficiencies, thermodynamic, 25. 
Efficiency and cost of electric generators 
and motors, 77 
and economy of gas engines, thermal, 

412 
economy and cost of steam engines 

and steam turbines, 49 
Efficiency and losses of steam turbine, 
48. boiler, 158 

of air compressors, volumetric, 526 
of a machine, 1 

of and losses in steam turbines, 48 
of gas engines mechanical, 409 
producers, 473 



584 



INDEX 



Efficiency of steam engines, mechanical, 49 
of the locomotive, 355 
of transmission, 321 
with oil fuel, boiler, 395 
with stack and mechanical draft 
systems, 185 
Electric developments, cost of hydro-, 
574 
drive vs. shafting and belting, 321 
generators and motors, 

efficiency and cost of, 77 
plants, cost of blast-furnace gas, 493 
power, cost of blast-furnace gas, 493 
in New York City, the cost of, 299 
Electricity, advantages and disadvant- 
ages of various fuels and, 399 
Elimination of the steam locomotive, 364 
Energy in fuels, cost of, 399 
of fuel, 15 

of wind and water, 6 
sources of, 1 
Enclosing direct-current motors, effects 

of semi and totally, 333 
Engine advantages, 71 

and turbine economy of combined, 60 
and turbine unit, combined, 48 
comparison of steam turbine with 

steam, 40 
conditions, special producer-gas, 458 
economy, steam, 51 
field of the reciprocating, 70 
flywheels, 35 
foundations proper, 84 
length of typical reciprocating, 19 
of the locomotive, the, 361 
Engine, piston speeds, gas, 408 
proper location for a gas, 420 
rapid development of the gas, 419 
the oil, 423 
the steam, 18 
Engines, applicability of, 71 

and steam turbines, efficiencies, 

economy and cost of steam, 49 
and turbines, fields of, 70 
average steam consumption of 

reciprocating steam, 51 
beam. 21 
classification of, by their use of 

steam, 22 
classified by position of cylinder axis, 
20 



Engines, compound and multiple-ex- 
pansion, 31 
condensing and non-condensing, 27 
cost of compound condensing, 69 
Corhss, 67 
of Diesel, 432 
of gas, 422 

of simple, high-speed, 63 
■ non-condensing Corliss, 64 
duty of pumping, 61 
economy tests of steam, 54 
expansive and non-expansive, 24 
four-cycle and two-cycle, 402 
high-speed, 23 
horizontal, 20 
horsepower of internal combustion, 

406 
internal combustion, 402 
low-speed, 23 
lubrication of internal combustion, 

417 
mechanical efficiency of gas, 409 

of steam, 49 
piston compressors and blowing, 520 
pressures and temperatures in in- 
ternal combustion, 415 
regulating or governing gas, 408 
rotary steam, 35 
single- and double-acting, 24 
solar, 12 

special classification of, 34 
starting gas, 420 
summary of general data on Diesel, 

432 
thermal efficiencies of different types 
of, 499 
efficiency and economy of gas, 412 
throttling and cut-off, 32 
turbines vs., in units of small ca- 
pacity, 71 
Engines, una-flow, 30 
vertical, 20 
weight of gas, 422 
Estimating boiler capacity required by 
office buildings, 348 
miscellaneous steam requirements 
in large buildings, 341 
Evaporation, factor of, 161 

per pound of dry coal, 162 
Evaporative condensers, 97 
Evase' stacks, 172 



INDEX 



585 



Examples of comparative cost of operat- 
ing different types of power in- 
stallations, 503 
Exciters for alternators, 332 

capacity required in, 332 
Exhaust heads and oil extractors, 229 

low-pressure or, bleeder and mixed 
pressure turbines, 46 

noises, 421 

pipe, 421 

piping, 224 

steam heating, cost of, 339 
Expansion joints, 111 

of pipe, 227 
Expansive and non-expansive engines, 24 
Expense of locomotives, fuel, 363 
Expenses, operating, 251 
Experiments with briquets, results of, 

381 
Explosions, boiler, 163a 
Extractors, scrubbers and tar, 457 



Factor, diversity, 274 
load, 272 

of evaporation, 161 
use, 275 
Factors affecting value of coal, 376 
Fans, capacity of, and power required, 

181 
Feed pipe, 129 
pumps, 196b 
centrifugal, 197 
cost of, 199 

steam consumption of, 196b 
water, boiler, 210 
-water heaters, 201 
cost of, 203 
impurities in, 211 
Feed water piping, 223 

treatment of, 213 
Field of the reciprocating engine, 70 
Fields of engines and turbines, 70 
Fires, time between periods of drawing 

467 
Fire-tube boilers, cost of, 134 
First cost vs. economy of operation, 74 
Fittings, pipe, 217 

Fixed gases, conversion of tarry vapors 
into, 451 



Flues and uptakes, 173 

average cost of stacks and, 178 
Flumes, head races, canals and, 567 
Flume, the Holyoke testing, 559 
Flywheels, engine, 35 
Foaming and priming, 212 
Forced and induced draft, 179 
Formula, Dulong's, 369 
Formulae for cost of condensers, 116 
Foundation bolts, 86 
Foundations, 83 

cost of concrete, 84 

engine, proper, 84 
Four-cycle and two-cycle engines, 402 
Fuel, 256 

-bed area, pounds of fuel per square 
foot of, per hour, 462 

bed, shooting the, 451 

boiler efficiency with oil, 395 

briquets, 374 

consumption and cost of operation 
of existing plants, actual, 509 

cost, station, 256 

cubic feet of gas per pound of, 
465 

energy of, 15 

expense of locomotives, 363 

for locomotives, powdered, 359 

oil under specifications, purchase of, 
396 

per horsepower per hour, pounds of, 
259 

per square foot of fuel-bed area per 
hour, pounds of, 462 

powdered, 384 

standby, 467 

used by producer-gas power plants, 
amount of, 461 

with different types of installations, 
relative cost of, 500 
Fuels, 366 

and of electricity, advantages and 
disadvantages of various, 399 

cost of energy in, 399 

heating value of, 374 

in gas producers, use of low-grade, 
461 

liquid, 390 

solid, 366 

used in gas producers, 459 

use of low-grade, 382 



586 



INDEX 



Fuels, weight and volume of solid, 375 
Furnace design, 140 

efficiency, boiler and, 158 

losses, 148 
Fusible plugs, 129 



Gage-cocks, water glass and, 129 
Gage, steam, 129 

Gain in steam consumption by condens- 
ing, probable, 52 
Gas, 397 

and gas producers, producer, 439 
composition of producer, 439, 463 
distribution, 490 
-electric plants, cost of blast-furnace, 

493 
-electric power, cost of blast-furnace, 

493 
engine conditions, special producer, 
458 
piston speeds, 408 
proper location for a, 420 
rapid development of the, 419 
engines, cost of, 422 

mechanical efficiency of, 409 
regulating or governing, 408 
starting, 420 
thermal efficiency and economy of, 

412 
weight of, 422 
for domestic heating, natural, 398 
generator, cleaning the, 466 
heat value of producer, 464 
installations, cost of producer-, 477 
per pound of fuel, cubic feet of, 

465 
plant operation of a typical down- 
draft producer, 449 
plants, byproduct coke-oven, 489 
byproduct producer-, 482 
operating results and working 
cost of byproduct producer-, 486 
relative cost of steam and pro- 
ducer, 478 
uses of tar from producer-, 468 
power, cost of steam and blast" 
furnace, 507 
Gas power plants, amount of fuel used 
by producer-, 461 



Gas power plants, producer, 439 

revolving eccentric-grate, 471 
the blast furnace as a, 491 
producer, cost of, 476 
dimensions of, 476 
efficiencj^ of, 473 
fuels used in, 459 
producer gas and, 439 



types of, 442 

use of low-grade fuels in, 461 
relative results from steam and pro- 
ducer, 475 
scrubbing the, 444 
turbines, 436 

under steam boilers, natural, 397 
utilization of water, 452 
various uses of producer-, 458 
Gases, conversion of tarry vapors into 
fixed, 451 
heating value of various, 396 
Gasoline, comparative results from de- 
natured alcohol and, 414 
Gating, 561 
General data on Diesel engines, summary 

of, 432 
Generator, cleaning the gas, 466 

speeds of turbine and, 569 
Generators, 330 

and motors, efficiency and cost of 
electric, 77 
Good operation, standards of, 291 
Governing gas engines, regulating or, 408 
Grading of pipe, 226 
Graphite, 366 
Grate area, pounds of coal per square 

foot of, per hour, 163 
Grates, chain, 151 

Gravity, energy of wind and water, 6 
Grouting, 86 
Guyed iron stacks, cost of, 177 



Handling, ash, 236 
coal, 232 

and ash, 232 
cost of ash, 237 
of coal, 235 
Hanging or supporting boilers, 133 
Head races, canals and flumes, 557 



INDEX 



587 



Heat balance for test locomotive, aver- 
age, 363 
methods of selling, 335 
value of producer gas, 464 
Heaters, cost of feed-water, 203 

feed-water, 201 
Heating and power, comparative costs of 
private and central station, 351 
cost of exhaust steam, 339 
district, 334 

natural gas for domestic, 398 
plant, the byproduct, 334 
purposes, producers, for metallurgi- 
cal and, 458 
station, 343 
steam system of, 344 
value of fuels, 374 

of various gases, 396 
water systems of, 344 
High-pressure drip piping and boiler 
returns, 223 
steam piping, 218 
-speed engines, 23 

cost of simple, 63 
Hints on steam plant operation, 316 
Holyoke testing flume, the, 559 
Horizontal engines, 20 
Horsepower, cost of a, at the machine, 326 
-hour, pounds of water per, 161 
of a cylinder, 18 

of internal combustion engines, 402 
of the locomotive, 355 
rating of boilers, 130 
Hotwells, 111 
Humphrey pump, the 433 
Hydraulic installations, cost of, 570 
power, 538 

-station layouts, 549 
Hydro-electric developments, cost of, 574 



I 



Ice making, 535 

Idle boilers, 163 

Impulse and reaction turbines, 40 

Impurities in feed water, 211 

Incidentals, 248 

Increased economy with increase of steam 

pressure in the locomotive, 357 
Individual condenser installations, cost 

of, 116 



Induced draft, forced and, 179 
Injector, the, 200 
Injectors, cost of, 201 
Inspection, boiler, 163a 
Installations, cost of, complete, 248 
cost of hydraulic, 570 
producer-gas, 477 
Insurance, taxes and, 255 
Interest, 253 

Internal combustion engines, 402 
horsepower of, 406 
lubrication of, 417 
pressures and temperatures in, 
415 
-combustion principle, advantages 

of the, 418 
disadvantages of the, 419 
Interpole or commutating-pole motors, 

329 
Iron stacks, cost of guyed, 177 
Isolated plant vs. central station power, 
496 



Jacket, use of water, 472 
Jet, air pumps, steam, 109 
Joints, expansion. 111 
pipe, 216 



K 



Kilovolt-amperes, apparent power, 332 

Kilowatts, rating in, 332 

Kinetic air-pump system, the, 108 



Labor, 259 

cost, station, 259 

of men, 2 
Leakage, radiation and, 209 
Lignite, 367, 460 
Liquid fuels, 390 
Load curves, 301 

factor, 272 

in tall office buildings, division of 
the, 347 
Location for a gas engine, proper, 420 

of power plant, 239 



588 



INDEX 



Locomotive as a whole, the, 361 

average heat balance for test, 363 

boiler performance, 360 

drawbar pull of the, 356 

efficiency of the, 355 

ehmination of the steam, 364 
Locomotive, horsepower of the, 355 

increased economy with increase of 
steam pressure in the, 357 

the engine of the, 361 

the power plant of the steam, 355 

tractive effort of the, 357 

tractive force of the, 355 
Locomotives, depreciation of, 358 

fuel expense of, 363 

mechanical stokers for, 358 

powdered fuel for, 359 
Loop, steam, 231 
Losses, furnace, 148 

in boiler plant Operation, principal, 

165 in steam turbines, efficiency of 
and, 48 

of steam turbines, efficiency and, 48 

standby, 277 
Low-grade fuels in gas producers, use of, 
461 
use of, 382 

-pressure or exhaust, bleeder and 
mixed pressure turbines, 46 

-speed engines, 23 
Lubrication of internal combustion en- 
gines, 417 



M 



Machine, cost of a horsepower at the, 
326 
efficiency of a, 1 
service, selection of motors and speed 

requirements for, 325 
tools, sizes of motors recommended 
to drive, 325 
Machinery, refrigerating, 533 
Maintenance, 263 
cost, station, 263 

of stacks and mechanical draft sys- 
tems, depreciation and, 184 
Materials, boiler, 126 
Maximum boiler pressure, 128 
Mechanical details of water turbines, 
560 



Mechanical draft, chimneys and, 166 

systems, depreciation and main- 
tenance of stacks and, 184 
efficiency with stack and, 185 
efficiency of gas engines, 409 

of steam engines, 49 
stokers, 148 
cost of, 164 
for locomotives, 358 
saving by use of, 163b 
Mechanically stirred and revolving 

grate producers, 469 
Men, labor of, 2 

muscular power of, and animals, 2 
Metallurgical and heating purposes, pro- 
ducers for, 458 
Method of sampling, 381 
Methods of motor drive, 322 

of selling heat, 335 
Mixed condensation, 87 

pressure turbines, low-pressure or 
exhaust, bleeder and, 46 
Motor drive, methods of, 322 
Motors, alternating-current, 329 

and speed requirements for machine 

service, selection of, 325 
animal, 4 
direct-current, types and where used, 

328 
effects of semi and totally enclosing 

direct-current, 333 
efficiency and cost of electric gene- 
rators and, 77 
interpole or commutating-pole, 329 
recommended to drive machine 

tools, sizes of, 325 
tide and wave, 10 
Multiple-expansion engines, compound 

and, 31 
Muscular power of men and animals, 2 

N 

Natural gas for domestic heating, 398 

under steam boilers, 397 
Noise of turbo-generators, 49 
Noises, exhaust, 421 

Non-condensing Corliss engines, cost of 
simple, 64 

engines, condensing and, 27 
Non-expansive engines, expansive and, 24 
Number of boilers to do given work, 163b 



INDEX 



589 



Office buildings, division of the load in 
tall, 347 

estimating boiler capacity required 
by, 348 

refrigeration for, 350 

selection of plant for tall, 347 

the power plant of the tall, 347 
Oil burners, 209 

engine, the, 423 

extractors, exhaust heads and, 229 

fuel, boiler efficiency with, 395 

in air compressor cylinders, 527 

pumps, 209 

required by steam turbines, 49 

under specifications, purchase of 
fuel, 396 

vs. coal under boilers, 392 

waste and supplies, 263 
Operating costs for different types of 
installations, comparative effi- 
ciencies and, 496 
of producer-gas power plants 
479 

different types of power installations, 
examples of comparative cost 
of, 503 

expenses, 251 

hints on steam plant, 316 

results and working costs of by- 
product producer-gas plants, 
486 
Operation and care of boilers, 165 

of a typical down-draft producer- 
gas plant, 449 

of existing plants, actual fuel con- 
sumption and cost of, 509 

standards of good, 291 
Output, ratings by, 332 



Peak loads, carrying economically, 283 

Peat, 370, 460 

Percentage of steam generated used by 

auxiliaries, 208 
Performance, locomotive boiler, 360 
Periods of drawing fires, time between, 

467 
Pipe coverings, 228 



Pipe exhaust, 421 

expansion of, 227 
feed, 129 
fittings, 217 
grading of, 226 
joints, 216 

sizes, determining, 225 
systems, disadvantages of various, 
219 
Piping, 215 

auxiliary steam, 218, 222 
cost of, 228 

details, boiler-room, 221 
exhaust, 224 
feed-water, 223 

high-pressure drip and boiler re- 
turns, 223 
steam, 218 
Piston compressors and blowing engines, 
520 
speed as distinguished from rotative 

speed, 23 
speeds, gas engine, 408 
Plant for tall office buildings, selection of, 
347 
of the steam locomotive, the power, 

355 
of the tall office building, the power, 

347 
operation, hints on steam, 316 
operation, principal losses in boiler, 
165 
Plugs, fusible, 129 
Ponds, cooling, 116 

spray, 117 
Position of cylinder axis, engines classi- 
fied by, 20 
Pounds of coal per square foot of grate 
area per hour, 163 
of fuel per horsepower per hour, 
259 
per square foot of fuel-bed area 
per hour, 462 
of water evaporated per pound of dry 

coal, 162 
of water per horsepower-hour, 161 
Powdered fuel, 384 

for locomotives, 359 
Power, annual cost of, 309 

comparative costs of private and 
central station heating and, 351 



590 



INDEX 



Power, cost of, 285 

blast-furnace gas-electric, 493 
of steam and blast-furnace gas, 
507 
hydraulic, 530 

in New York City, the cost of elec- 
tric, 299 
installations, examples of compara- 
tive "cost of operating different 
types of, 503 
of men and animals, muscular, 2 
plant, analysis of development in a, 
16 
arrangement of the, 242 
constructions, 239 
Power plant, design of, 239 
location of, 239 

of the steam locomotive, the, 355 
of the tall office building, the, 347 
the steam, 239 
plants, amount of fuel used by pro- 
ducer-gas, 461 
operating costs of producer-gas, 
479 
required by producer auxiliaries, 467 

for condenser pumps, 113 
stations, comparative cost of steam, 

complete, 250 
transmission, 320 
unit of, 1 
Pressure, effect of speed on average 
steam, 357 
in the locomotive,increased economy 

with increase of steam, 357 
maximum boiler, 128 
producer, the up-draft, 447 
Pressures and temperatures in internal 

combustion engines, 415 
Preventing scale, 212 
Priming, 111 

foaming and, 212 
Principal losses in boiler plant operations, 

165 

Principles of steam turbines, basic, 39 

Private and central station heating and 

power, comparative costs of, 351 

Probable gain in steam consumption by 

condensing, 52 
Problems, 75a, 81, 86a, 120, 165a, 189, 
214a, 231a, 265, 284, 315, 354, 
400, 437, 494, 537 



Producer auxiliaries, power required by, 
467 
gas, 439 

and gas producers, 439 
composition of, 439, 463 
engine conditions, special, 458 
heat value of, 464 
installations, cost of, 477 
plant, operation of a typical down- 
draft, 449 
plants, byproduct, 482 

operating results and working 

costs of byproducts, 486 
relative cost of steam and, 478 
uses of tar from, 468 
power plants, amount of fuel used 
by, 461 
operating costs of, 479 
Producer gas, relative results from steam 
and, 475 
various uses of, 458 
revolving eccentric-grate gas, 471 
the blast furnace as a gas, 491 
the double-zone, 455 
the down-draft, 449 
the up-draft pressure, 447 
suction, 438 
Producers, advantages of revolving-grate, 
472 
cost of gas, 476 
dimensions of gas, 476 
efficiency of gas, 473 
for metallurgical and heating pur- 
poses, 458 
fuels used in gas, 459 
mechanically stirred and revolving- 
grate, 469 
producer gas and gas, 439 
slagging gas, 488 
types of gas, 439 
use of low-grade fuels in gas, 461 
Proper location for a gas engine, 420 
Proportions of turbines and runners, de- 
sign and, 555 
Pull of the locomotive, drawbar, 356 
Pump, air-lift, 525 

the Humphrey, 433 
Pumping engines, duty of, 61 
Pumps, centrifugal feed, 197 
circulating, 99 
condensate, 100 



INDEX 



591 



Pumps, cost of feed, 199 

feed, 196b 

oil, 209 

power required for condenser, 113 

steam consumption of feed, 196b 

steam jet, air, 109 
Purchase of coal, specification standards 
for, 377 

of coal under specifications, the, 375 

of fuel under specification, 396 



Revolving eccentric-grate gas producer, 
471 
-grate producers, advantages of, 472 
mechanically stirred and, 469 

Rope driving, 320 

Rotary steam engines, 35 

Rotative speed, piston speed as dis- 
tinguished from, 23 

Runners, design and proportions of tur- 
bines and, 555 



Radiation and leakage, 209 

Rapid development of the gas engine, 

419 
Rated current, 332 
Rating, boiler, 158 
in kilowatts, 332 
of boilers, horsepower, 130 
of steam turbines, 48 
Ratings by output, 332 
Reaction turbines, impulse and, 40 
Readiness to serve, 275 
Reciprocating engine, field of the, 70 
length of typical, 19 
steam engines, average steam con- 
sumption of, 51 
Refrigeration for office buildings, 350 
Refrigerating machinery, 533 
Regulating or governing gas engines, 

408 
Regulation, waterwheel, 562 
Relative cost of fuel with different types 
of installations, 500 
cost of steam and producer-gas 

plants, 478 
results from steam and producer gas, 
475 
Reliability and conservation, 496 
Results and working costs of byproduct 
producer-gas plants, operating, 
486 
from denatured alcohol and gasoline, 

comparative, 414 
from steam and producer gas, rela- 
tive, 475 
of experiments with briquets, 381 
Return-tubular boilers, 122, 125 
Returns, high-pressure drip piping and 
boiler, 223 



Safety valves, 129 

Sampling, method of, 381 

Saving by use of mechanical stokers, 163b 

coal in steam power plants, 496 of 

space with turbines, the, 72 
Scale, preventing, 212 
Scrubber water required, 468 
Scrubbers and tar extractors, 457 
Scrubbing the gas, 444 
Selection of boiler type, 163b 

of motors and speed requirements 
for machine service, 325 

of plant for tall office buildings, 347 
Selling heat, methods of, 335 
Semi-bituminous coals, 367 
Separators, steam, 231 
Serve, readiness to, 275 
Settings, boiler, 130 
Shafting and belting, 320 

cost of, 320 

electric drive vs., 321 
Shooting the fuel bed, 451 
Simple, high-speed engines, cost of, 63 
non-condensing Corliss engines, cost 
of, 64 
Single- and double-acting engines, 24 
Sizes of motors recommended to drive 

machine tools, 325 
Slagging gas producers, 488 
Small steam turbines, steam consump- 
tion of, 58 

turbines, 45 
Smoke and smoke prevention, 190 

effects of, 192 

reduction, coal byproducts and, 196a 
Solar engines, 12 
Solid fuels, 366 

weight and volume of, 375 



592 



INDEX 



Soot blowers, 214 

Sources of energy, 1 

Space required by boilers, 139 

the saving of, with turbines, 72 
Special chimneys, cost of, 178 
classification of engines, 34 
producer-gas engine conditions, 458 
Specification standards for purchase of 

coal, 377 
Specifications for boiler construction, 128 
purchase of fuel oil under, 396 
the purchase of coal under, 375 
Speed, effect of, on average steam pres- 
sure, 357 
piston, as distinguished from rotative 

speed, 23 
requirements for machine service, 
selection of motors and, 325 
Speeds, gas engine piston, 408 

of turbine and generator, 569 
steam, 221 
Spillways, 548 
Spray ponds, 117 
Stack and mechanical draft systems 

efficiency with, 185 
Stacks and flues, average cost, 178 

and mechanical draft systems, de- 
preciation and maintenance of, 
184 
Stacks, cost of guyed iron, 177 

Evase, 172 
Standards for purchase of coal, speci- 
fication, 377 
of good operation, 291 
Standby fuel, 467 

losses, 277 
Standpipe, water tower or, 569 
Starting gas engines, 420 
Station cost, 256 

design, central, 276 

types of, 244 
fuel cost, 256 
heating, 343 
labor cost, 259 
layouts, hydraulic-, 549 
maintenance cost, 263 
Steam and blast-furnace gas power, cost 
of, 507 
and producer-gas plants, relative 
cost of, 478 
relative results from, 475 



Steam and water turbines, difference be- 
tween, 39 
boiler, the, 121 

boilers, natural gas under, 397 
classification of engines by their use 

of, 22 
consumption by condensing, prob- 
able gain in, 52 
consumption of feed pumps, 196b 
of reciprocating steam engines, 

average, 51 
of small steam turbines, 58 
probable gain in, by condensing, 51 

variable-load, 61 
engine, comparison of steam turbine 
with, 40 
economy, 51 
the, 18 
engines and steam turbines, efficien- 
cy, economy and cost of, 49 
engines, average steam consumption 
of reciprocating, 61 
economy tests of , 54 
mechanical efficiency of, 47 
rotary, 35 
gage, 129 

heating, cost of exhaust, 339 
jet, air pumps, 109 
locomotive, elimination of the, 364 

the power plant of the, 355 
loop, 231 

piping, auxiliary, 218, 222 
piping, high pressure, 218 
plant operation, hints on, 316 
power plant, the, 239 
saving coal in, 496 
stations, comparative cost of, com- 
plete, 250 
pressure, effect of speed on average, 
357 
in the locomotive, increased econ- 
omy with increase of, 357 
reqtiirements in large buildings, esti- 
mating miscellaneous, 341 
separators, 231 
speeds, 221 

system of heating, 344 
transmission, 321 
traps, 231 

turbine, comparison of, with steam 
engine, 40 



INDEX 



593 



Steam turbines, 39 

basic principles of, 39 

cost of, 69 

efficiency, economy and cost of 

steam engines and, 49 
efficiency of and losses in, 48 
oil required by, 49 
rating of, 48 

steam consumption of small, 58 
used by auxiliaries, percentage of, 208 
use of superheated, 358 
Stokers, cost of mechanical, 164 

for locomotives, mechanical, 358 
mechanical, 148 

saving by use of mechanical, 163b 
types of, 149 
Stop valve, 129 
Storage batteries, water, 554 
coal, 237 
cold, 536 
Straw, 373 

Suction producer, the up-draft, 442 
Summary of general data on Diesel 

engines, 432 
Superheated steam, use of, 358 
Supplies, oil, waste and, 263 
Supporting boilers, hanging or, 133 
Surface condensation, 90 
System, the kinetic air-pump, 108 



Tall office building, the power plant of 

the, 347 
buildings, division of the load in, 347 
Tall office buildings, selection of plant 

for, 347 
Tan bark, 372 
Tar extractors, scrubbers and, 457 

from producer-gas plants, uses of, 

468 
Tarry vapors, conversion of, into fixed 

gases, 451 
Taxes and insurnace, 255 
Temperature in internal combustion 

engines, pressures and, 415 
Testing flume, the Holyoke, 559 
Test locomotive, average heat balance 

for, 363 
Tests of steam engine, economy, 54 
of turbines, economy, 59 



The blast furnace as a gas producer, 491 

byproduct heating plant, 334 

cost of electric power in New York 
City, 299 

down-draft producer, 449 

double-zone producer, 455 

engine of the locomotive, 361 

Holyoke testing flume, 559 

Humphrey pump, 433 

injector, 200 

kinetic air-pump system, 108 

locomotive as a whole, 361 

oil engine, 423 

power plant of the steam locomotive, 
355 
of the tall office building, 347 

purchase of coal under specifications, 
375 

saving of space with turbines, 72 

steam boiler, 121 
engine, 18 
power plant, 239 

up-draft pressure producer, 444 

up-draft suction producer, 442 
Thermal efficiencies of different types of 
engines, 499 

efficiency and economy of gas en- 
gines, 412 
Thermodynamic efficiencies, 25 
Throttling and cut-off engines, 32 
Tide and wave motors, 10 
Tie-rods, buck-stays and, 132 
Time between periods of drawing fires, 

467 
Tools, sizes of motors recommended to 

drive machine, 325 
Torpedo-boat service, briquets in, 382 
Tower of standpipe, water, 569 
Towers, cooling, 117 

cost of cooling, 119 
Tractive effort of the locomotive, 357 

force of the locomotive, 355 
Transmission, efficiency of, 321 

power, 320 

steam, 321 
Traps, steam, 231 
Treatment of feed water, 213 
Tubes, draft, 561 
Turbine advantages, 70 

and generator, speeds of, 569 

commercial aspects of the, 70 



594 



INDEX 



Turbine advantages, comparison of 
steam, with steam engine, 40 
economy of combined engine and, 

60 
unit, combined engine and, 48 
Turbines and runners, design and 

proportions of, 555 
applicability, 71 
basic principles of steam, 39 
casings of water, 561 
classification of, 40 
condensing apparatus for, 95 
cost of steam, 69 
difference between steam and water, 

39 
economy tests of, 59 
efl&ciency of and losses in steam, 

48 
fields of engines and, 70 
gas, 436 

impulse and reaction, 40 
low-pressure or exhaust, bleeder and 

mixed pressure, 46 
mechanical details of water, 560 
oil required by steam, 49 
rating of steam, 48 
small, 45 
steam, 39 

consumption of small steam, 

58 
the saving of space with, 72 
vs. engines in units of small capacity, 

71 
Turbo-generators, noise of, 49 
Two-cycle engines, four-cycle and 

402 
Types of boilers, 121 

of gas producers, 439 
of installations, comparative effi- 
ciencies and operating costs for 

different, 496 
relative cost of fuel with different, 

500 
of power installations, examples of 

comparative cost of operating 

different, 503 
of station design, 244 
of stokers, 149 
Typical down-draft producer-gas plant, 

operation of a, 449 
reciprocating engine, length of, 19 



u 

Una-flow engines, 30 

Unit, combined engine and turbine, 48 

of power, 1 
Units of small capacity, turbines vs. en- 
gines in, 71 
Up-draft pressure producer, the, 444 

suction producer, the, 442 
Uptakes, flues and, 173 
Use factor, 275 

of briquets, 381 

of low-grade fuels, 3.82 
in gas producers, 461 

of mechanical stokers, saving by, 
163b 

steam, classification of engines by 
their, 22 

of superheated steam, 358 

of water jacket, 472 
Uses of producer-gas, various, 458 

of tar from producer-gas plants, 468 
Utilization of water gas, 452 



Value of coal, factors affecting, 376 
of fuels, heating, 374 
of producer gas, heat, 464 
of various gases, heating, 396 
Valve, stop, 129 
Valves, 217 

safety, 129 
Vaporizers, 456 
Vaporizer water required, 467 
Vapors, conversion of tarry, into fixed 

gases, 451 
Variable load economy, 269 

steam consumption, 61 
loads, cost curves at, 302 
Various pipe systems, disadvantages of, 
219 
uses of producer-gas, 458 
Vertical engines, 20 
Volume of solid fuels, weight and, 375 
Volumetric efficiency of air compressors 
526 

W 

Waste and supplies, oil, 263 
Water, 264 

boiler feed, 210 



INDEX 



595 



Water, circulating, 416 

cost of, 120 

energy of wind and, 6 

evaporated per pound of dry coal, 
pounds of, 161 

gas, utilization of, 452 

glass and gage-cocks, 129 

impurities in feed, 211 

jacket, use of, 472 

per horsepower-hour, pounds of, 
161 

required, scrubber, 468 
vaporizer, 467 

storage batteries, 554 

systems of heating, 344 
Water tower of standpipe, 569 

treatment of feed, 213 

tube boilers, 123, 125 



Water tube boilers, cost of, 135 
turbines, casings of, 561 

difference between steam and, 39 
mechanical details of, 560 
Waterwheel regulation, 562 
Wave motors, tide and, 10 
Weight and volume of solid fuels, 375 
of boilers, 139 
of gas engines, 422 
When buying coal, 375 
Wind and water, energy of, 6 
Windmills, 6 

capacity of, 8 
economy of, 9 
Wood, 371 

Working costs of byproduct producer- 
gas plants, operating results 
and, 486 



i 



